MC Choice Changing / Backend / Communications: notifications, banners, comments, etc.

When an option is added, we set the user's forecast to terminate at the end of the grace period. This needs to be communicated to forecasters with excellent clarity and plenty of warning.
Also good to communicate when one is removed, but likely only by comment - there isn't really a call to action.

Proposal

all wordings are TBD

• any change:
  • a comment should be posted as such
• If choice is added:
  • email goes out next day (why not immediate? that's a lot of extra work to be able to revert this change!)
  • schedule an email to go out day before end of grace period, but cancel the email if they forecast during the grace period
  • banner: "call to action"
  • feed tile: "call to action"
  • prediction flow: a "todo"
• update FAQ about this process including scoring and data storage etc.

TODO

• on option delete
  • send immediate notification
  • post comment
• on option add
  • send immediate notification
  • post comment
  • schedule an email for day before end of grace period
  • add banner to post calling to action
  • (nice to have) add feed tile chip
  • (nice to have) add "todo" to prediction flow
• on option rename
  • do nothing (this is most likely a spelling change, so it shouldn't require notification)
• on forecast during grace period
  • cancel scheduled email
  • remove banner for user
  • (only if feed tile chip feature is added) remove feed tile chip for user
• FAQ update
  • TBD