Input error checks added: plotSpectrum, plotMD, plotBin, re #8419
Better error messages, re #8419
New mantidplotpy test: MantidPlotInputArgsCheck, re #8419
remove reminder comment, re #8419
Catch (good) exceptions so that jenkin's tests don't fail, re #8419
with_invalid_raises_RuntimeError -> raises_ValueError, re #8419
Merge remote-tracking branch 'origin/bugfix/8419_better_input_check_for_python_plots'