Re #6192. Remove python createSpectraAxis methods (in API v1 & v2).

This is in preparation for changes to the SpectraAxis class, which
will make it impossible to create an axis of this type without a
parent workspace.
The removed methods are unused anyway.
Re #6192. Eliminate spectrum no. duplication between Axis & ISpectrum

Achieved by having the SpectraAxis class hold a pointer to it's owning
workspace and going through that back to the spectrum number held by
the ISpectrum when necessary.
Other code and tests need to be fixed after these changes.
Re #6192. Fix code & tests for changes in SpectraAxis class.
Re #6192. Fix formatting/indentation only. No code changes.
Re #6192. Remove redundant setting of spectrum number.

The workspace factory will have already done it in these circumstances.
Re #6192. Fix formatting/indentation only. No code changes.
Re #6192. Remove redundant setting of spectrum number.

The workspace factory will have already done it in these circumstances.
Re #6192. Prefer setting spectrum number via ISpectrum class.

Rather than going via the axis. The remaining uses of Axis::setValue
in this package are where the axis is (or could be) a NumericAxis.
Re #6192. Prefer setting spectrum number via ISpectrum class.
Re #6192. Prefer setting spectrum number via ISpectrum class.

Rather than going via the axis.
Re #6192. Fix for non 1-1 spectra-detector mapping in padSpectra.

Code taken from the former SpectraAxis 'constructor from a SpectraDetectorMap'.
This correctly handles ISIS instruments where multiple detectors contribute
to a spectrum. This code will hopefully only be temporary pending the elimination
of the SpectraDetectorMap (in #6191).
Merge branch 'feature/6192_remove_spectrum_no_duplication' into develop

Re #6192.
Conflicts:
	Code/Mantid/Framework/PythonInterface/mantid/api/src/Exports/Axis.cpp