website/admin: implement schedule edit notifications

[icxes]

For editing the schedule, there should be 2 things

• a page in /admin where admins can edit the schedule (set/remove/change dj and maybe edit description?) for each day
• a page where a DJ on the schedule can edit their own description
  • also possibly remove themselves from their own day, or mark themselves as inactive?
  • this could just be their profile page

I had thought we could just use the djtext field from the djs table instead of having a separate column for it in the schedule table, since that would also let people who are currently not on the schedule set a description. We already need the djimage for each user from the djs table anyway.

[Wessie]

/admin/schedule is now implemented, but the way it is implemented should probably be changed such that when setting an owner the user can change the schedule text instead of using dj.text

[Wessie]

The current implementation also doesn't let us be aware of when a schedule was updated exactly so we can't do notifications right now