Include the ability to select place closure in setting the parameters for Imperial model

[aeisenberg]

From the last paragraph here: https://github.com/covid-modeling/model-runner/issues/39#issuecomment-634656983 It's clear that our results for the Imperial model will improve if we can set Place Closure levels along with School closure levels. There are still some open questions about it:

1. Should we separate out Place closure in a different section in the UI? Ie- should it be possible to set place closure independently from school closure? Or should we ensure the two are always set together?
2. Are there any backwards compatibility issues we need to think about?