Add Cropping Options to Eng Diff Calib Tab

Switch to JSON Parser for SANS State

Re Expose getting time averaged std to python

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

Remove Confusion from SaveNISTDAT example 

Create total scattering pdf rebin output

Windows: Fix switching between Python 2/3 without clean

Also uses fin_package rather than handwritten code to find
Python libraries so unsetting code works as expected.

I've added the link back in as the saveNISTDAT_data.nxs file was already in the DocTest data file and had just been removed from the usagedata so this was the simplest thing to do. This file is now in the UsageData

Fixing crash with fit constraints in the Muon Analysis 2 GUI

Also fixes behaviour where deprecated functions actually
no longer did what they used to do.
Refs #27736

Allow switching between Python 2/3 without cleaning CMake configuration

Add option to set PDF type on polaris create_total_scattering_pdf

This is the same as mantidplot

The attribute has become readonly in matplotlib 3.1 and setting
it raises an AttributeError. It is unused anyway and a hangover
from old code.
Refs #27736

Controls whether the build is against Python2 or Python3.
CMake checks have been introduced to flush out old variables
if a previous build was against a different python major.minor
version.

re #27554