Runs clang-tidy pass by ref across the codebase to fix-up various
warnings we are seeing in cppcheck

Also updated class_maker.py

This commit replaces all header guards in DataHandling with #pragma once

The format of the sample environment xml file has been extended to support
loading a .stl file for each environment component. An example spec file
has been created in ISIS/Pearl.xml. This can be used when running the
Algorithm SetSample
Various SampleEnvironmentXXX units have been moved out the Geometry package
into the DataHandling package to facilitate this because they needed to
access the STL loading code in DataHandling
SetSample contains some features for overriding the sample geometry if the
geometry is a CSGObject. This has been sidestepped for mesh geometries.
The methods setId and setMaterial have been moved up to IObject because
it's useful to have them applicable to all objects (CSG, mesh)
Some of the repeated code in SetSample, LoadSampleEnvironment (and now
SampleEnvironmentSpecParser) has been centralised in a new class LoadStlFactory
Also changed container logic so that if there's only one container specified
in the env spec file you don't need to specify it in SetSample
Centralise code relating to scaling mesh vertices and handling of units
into the LoadShape class and rename it MeshFileIO now that SaveStl is also
descended from this class
Move repeated code to choose Ascii or binary STL reader into a factory class