Formatting changes only.

Refs #10470
Fix coverity warning about variable initiliaization.

Refs #10470
Use int64 for omp loop variable.

Refs #10470
First set of refactorings.

Refs #10470
Continuing with refactoring:

* Start to functionalise the algorithm
* Follow coding standard for member variables names
Refs #10470
Refactor a few more parts in to methods.

Refs #10470
Move main calculation into a method.

Refs #10470
Use references when returning event lists.

This gives a speed gain ~80%
Refs #10470
Use VectorHelper::SimpleAverage functor in computing average position.

This avoids 2 loops over the same data. Also, the non-HKL dimension
values don't change with each intersection so only copy them
over once.
Refs #10470
Alter function signature to just accept theta and phi

Refs #10470
Use detector grouping from ExperimentInfo

For workspaces with grouped detectors it now only considers the first one
from the group in the main loop but calculates the intersections using
the whole group.
Refs #10470
Merge branch 'master' into feature/10470_grouped_dets_sxdnorm

Conflicts:
	Code/Mantid/Framework/MDAlgorithms/inc/MantidMDAlgorithms/MDNormSXD.h
	Code/Mantid/Framework/MDAlgorithms/src/MDNormSXD.cpp

Refs #10470
Merge branch 'feature/10470_grouped_dets_sxdnorm' into develop