Fix Python unit tests under Python 3

Indirect Data Analysis - Fix Elwin integration range bars

Fix warnings from -Wpessimizing-move

Add usage tracking for interfaces

HistogramData module

Refs #16258

Move project loading and saving code out of ApplicationWindow

Indirect Diffraction - OSIRIS Diffspec calibration file option

Previous refactoring changed the last x value, did not seem to make a
difference though.

Fix small buffer overrun in FitTest

Some algorithm calls required an integer input but the future division
now returns a float. These calls have been wrapped in int()

This is supported by all of our numpy versions.

Reduce 'using namespace' in headers

Simplify MayersSampleCorrection usage example

Also removed misleading comments about clearing MRUs. Clearing MRU not
necessary for Dx, and cleared automatically by EventList::dataX.

The order of dict.keys() cannot be relied on. The docs say
it is undefined but the Python 2 implementation happened to
have a defined order

Align and focus empty

Add Project Serialisation Tests

Refs #14794

Fix larmor loading multiperiod event data

Refs #14794

Refs #14794