226 Reconnect ssp_scenario parameter between front-end and back-end

[LukeParky]

DESCRIPTION OF PR: Closes #226 I noticed that the SSP scenario front-end was not hooked up correctly. So using this code, I restricted the valid values to only ones I know will work. It may not be as powerful but it's working and much more user-friendly.

This is in preparation for our next release.

Developer Checklist

• [x] Make code change
• [ ] Update tests
  • [ ] Update / create new tests
  • [ ] Ensure these tests have the expected behaviour
  • [ ] Test locally and ensure tests are passing
• [x] Update documentation
  • [ ] Readme
  • [x] Docstrings
  • [x] Comments
  • [ ] Wiki

Reviewer Checklist

• [ ] Check new code for code smells
• [ ] Check new tests
  • [ ] Ensure adequate coverage
  • [ ] Check for code smells within tests
• [ ] Check if documentation needs updating
  • [ ] Readme
  • [ ] Docstrings
  • [ ] Comments
  • [ ] Wiki

[LukeParky]

Hi @caseyli92, this is ready for review again when you're available.