A few changes to fix handling of dates on client-side

* Fix UTC conversions in Meeting date/time selectors
* Add alternative format for dates (for skipping the timezone
  correction)
* Skip timezone correction when datetime string already contains the
  zone information
Set `context` for new Meetings in Interview Responses
Merge pull request #846 from reciprocity/feature/fix-some-dates

Fix some date handling; fix Meeting contexts