Parse date from the XML file.

Plus minor fixes to code layout.

Refs #7814
Make the algorithm use date to load the right IDF.

Plus some code clean-up.

Refs #7814
Update EMU instrument groupings.

That's apparently the only one which need to be changed, as has instrument
versions with different number of detectors.

Refs #7814
Renamed meaningless 'date' attribute to 'valid-on'.

Refs #7814
Merge remote-tracking branch 'origin/master' into feature/7814_grouping_date_parameter

Conflicts:
	Code/Mantid/Framework/DataHandling/src/LoadDetectorsGroupingFile.cpp
Let getInstrumentFilename method handle the empty date case.

Refs #7814
Renamed attribute to something even more meaningful.

Refs #7814
Added a unit test for a use case.

Plus some code cleaning.

Refs #7814
Merge branch 'feature/7814_grouping_date_parameter' into develop