Add support for a Python 3 build on RHEL 7

Fix bundling Python on Windows

Rework Abins broadening

Add Cropping Options to Eng Diff Calib Tab

Switch to JSON Parser for SANS State

Re Expose getting time averaged std to python

Refs #27631

A variable that was expected to be local was removed
by accident.
Refs #27744

Disable the plotting context menu options if a matrix ws has 1 bin

Switches to using the JSON library for parsing SANS state objects. This
provides numerous advantages:

- We do not need to maintain a custom (de)serializer
- JSON is a documented standard
- We can switch to type hinting in Python 3, currently a significant
amount of CPU time is spend reverifying typed params
- History becomes less brittle and will work from top level algorithms
- Allows new code to be written in a more Pythonic way (e.g. not forced
to use class level variables for them to be serialized)

Fix bug with dummy detectors in MayersSampleCorrection

Flips D22 and D33 detector pixel numbering

If the user defined a list of spectra to use that were not sequential,
the algorithm would take tha max and min values rather than the actual
list of specta. Eg "10-19, 50-59" would have resulted in the spectra
10-59 being used, which broke the algorithm.

Also included code suggestion
I've not removed the ability to plot from the Show data table because:
1. If they try that hard they deserve an empty graph
2. I can't work out how.

Fix sliceviewer for matplotlib 3.1

Fix settings test for python 3 in windows

Expand ISIS reflectometry system tests

See commit notes for CASTEP data update

Reference files for data import need updating for new advanced params

Test data needs updating due to changes in the Advanced
Parameters. Have eyeballed some of the file changes and the changes
seem fine. (There's also an increase in the written precision of atom
positions, but that will be related to the new test data writer.)

CASTEP data updated here, other codes to follow.

Abins uses a base class for Instruments, which defines a couple of
methods returning None. None is not the right response if these
methods were not adapted to a child class; use NotImplementedError to
mark these more clearly.

(And a typo in one of the test cases.)

The initial implementation assumed that the input series of sigma
values would monotonically increase, which is reasonable for TOSCA but
not for other instruments.

The logic is modified so that instead of
the input data, the list of sigma values used for convolution is
required to be sorted. As this list was generated within the same
function and ranges from (min(sigma), max(sigma)), the condition is
always satisfied.

The unit tests are not affected, but there may be a small numerical
difference as another implementation detail has been fixed in the
process; the interpolation x-values ('sigma factors') should be the
ratio between sigma and sigma at the lower bound of the current
window. In the initial implementation this was mistakenly identified
as sigma_chunk[0], the left-most value in the block _out of the actual
sigma values_; it should be the exact convolved width from `sigma_samples`.

A new method is provided in AbinsModules.CalculateS to generate a test
data file for the AbinsCalculateSPowder test. This format isn't great
and should be refined to something like standard JSON, but at least we
now have a standard way of generating it. The input options are a few
calculation parameters and a precalculated AbinsData object.

To make these objects easier to instantiate, a from_calculation_data()
classmethod is added.  The logic for identifying and calling a file
loader has been moved from the main Abins algorithm into AbinsData to
support this without redundancy. It may make sense to move this again
to somewhere else, e.g. a new *AbinsModules/Loaders/__init__.py* but
for now this is close to the point of use.

Equivalence of this method's output to the existing test file has been
verified manually for the Si2 order-1 test data. The reference file
does not need to be updated, and tests should continue to pass.

The sample data for the CalculateSPowder test needs to be updated as
part of the work on broadening, because Abins is now producing
different results. Specifically: the instrumental broadening function
applied to the S data has been replaced and is now smooth; the
reference frequencies are now defined to be in the middle of the
histogram bins rather than at the edges. This difference in binning
conventions has actually changed the size of the results array (by 1!)

The format of the sample data for CalculateSPowder is not very pretty;
it is some kind of raw text dump. It would be nice to avoid such
things with a proper JSON serialisation setup, but for now the
priority is to fix the test in a way that is comparable with previous
behaviour. The process used to generate the replacement file was to
obtain the calculation data with

  AbinsModules.CalculateS.init(...args...).get_formatted_data()

and dump the text representation to a file with

  numpy.set_printoptions(threshold=numpy.nan)
  with open('Si2-sc-CalculateSPowder_S.txt', 'w') as f:
      f.write(str(calculated_data.extract()))

The resulting file appears more neatly formatted than its predecessor
4b77bac3f8c1dc54f63bd41ca3075c48, but seems acceptable to the test parser.

Normalise Gaussians by multiplying by bin-width instead of dividing by
sum(values). The sum approach can go badly wrong if values lie near or
beyond the sampling range, as as tail fragment (or noise floor!) would
be amplified to unity. Scaling by the theoretical value as we do here
has a different downside: truncated broadening kernels will not quite
sum up to 1, so a little intensity is lost in broadening. This error
is more tolerable, especially as it can be decreased by extending the
truncation range.

To avoid polluting the dev-docs with algorithm-specific info and to
avoid storing/updating many image files the Abins development notes
are moved back into Concepts. The fast broadening method is broken
into a separate document to avoid too much wading through plots.