Refs #10227.  Implementation in progress.

On branch feature/10227_gui_filter_events
Changes to be committed:

      modified:   ../Mantid/scripts/FilterEvents/MainWindow.ui
      modified:   ../Mantid/scripts/FilterEvents/Ui_MainWindow.py
      modified:   ../Mantid/scripts/FilterEvents/eventFilterGUI.py
Merge branch 'feature/10227_gui_filter_events' into develop