Merge remote-tracking branch 'origin/bugfix/8286_ConvFit_delta_func_error'
Merge remote branch 'origin/bugfix/8056_event_performance'
Merge remote branch 'origin/feature/8221_schema_version'
Merge remote-tracking branch 'origin/bugfix/8279_fix_plot_spectra_for_groups_and_multiple_workspace'
re #8294: SANS window remove double addition of delete observer

This cause the Mantid to crash when you close and reopen the SANS interface
and perform some reduction.
Merge branch 'bugfix/8294_sans_crash_deleting_wks' into develop