Add new algorithm: CalculateResolution.

This algoritm is to replace the calcRes function found in refl_gui.py.
It is used to calculate the resolution (dq/q) for reflectometry, given
the instrument and a value of theta.

Refs #10007.
Add documentation for CalculateResolution.

Refs #10007.
Add unit test for CalculateResolution.

Refs #10007.
Replace calcRes with CalculateResolution.

Refs #10007.
Remove orphaned function from refl_gui.py

Refs #10007.
Parameterize strings in CalculateResolution.

Refs #10007.
Rename theta to two theta for clarity.

Refs #10007.
Only fetch instrument once.

Refs #10007.
Make CalculateResolution orientation agnostic.

Refs #10007.
Optimise CalculateResolutionTest.

Refs #10007.
Merge branch 'master' into feature/10007_make_resolution_calculation_more_robust

Conflicts:
	Code/Mantid/scripts/Interface/ui/reflectometer/refl_gui.py
Merge remote-tracking branch 'origin/feature/10007_make_resolution_calculation_more_robust'
refs #10007. Not quite wired up correctly.