Re #6191. Clear cppcheck warnings for this file.

Also a couple of other tidy-ups.
Re #6191. Tidy up includes.
Re #6191. Fix some errors in the test.

Seems like a holdover from older code - args that were really boolean were
being declared as ints and there was a problem if one path of an if-else
was taken (it isn't at present but will be shortly).
Re #6191. Add a method to resize the workspace to a specified size.

Also amend padSpectra() to resize to the number of detectors in the
instrument rather than using the SpectraDetectorMap. Of the 2 usages of
this method, one (SNSLiveEventDataListener) shouldn't care and the other
will be changed shortly so this is what we want.
Re #6191. Eradicate use of the SpectraDetectorMap in LoadEventNexus.
Re #6191. Remove unnecessary mentions of the spectra-detector map.
Re #6191. Remove use of SpectraDetectorMap from LoadSpice2D.
RE #6191. Test for detector ID.
Re #6191. Remove usage of SpectraDetectorMap.