Delete Timer (for when ensemble is over)

[tedyoung]

• [x] Replace current "Create Timer" button with an hx-load + hx-get to load the current button based on server state

  • [x] Add "Delete Timer" button on Admin's Ensemble Details Page (enabled if the timer for this ensemble was created)
  • [x] Disable the "Create Timer" button if the timer has already been created for this (or any other) ensemble
  • [x] EnsembleTimerHolder delete functionality
    • [x] Remove timer from EnsembleTimerHolder
    • [x] Clean up timer before deleting it (turn off seconds ticker, shutdown broadcaster?, anything else?)
    • [x] Handle situation of secondsTicker calling handleTickFor with an EnsembleId that does not (no longer?) have an existing timer: stop the secondsTicker and log the problem

• [ ] If Participant member refreshes the Timer page after the timer has been deleted, warning page will be displayed indicating that the ensemble is over and the timer is gone.

  • [ ] (Future) Display an "analytics" page for the ended ensemble