Fixed Doxygen commenting

Refs #4443
Implemented the method

Refs #4443
Implemented Unit tests

Refs #4443
Added some code so it is possible to test from MantidPlot

Refs #4443
Moved debugging code to more appropriate place

Refs #4443
Merge branch 'feature/4443_rectangular_detectors' into develop

Conflicts:
	Code/Mantid/Framework/Geometry/src/Instrument.cpp

Refs #4443