More general move up/down table cells
Move carousel slides up and down in list
Schedule carousel slides to be active from and until given times
Admin set active from/until datetimes
Initialise slide's active_until into the far future
Merge branch 'develop'

* develop:
  Initialise slide's active_until into the far future
  Admin set active from/until datetimes
  Schedule carousel slides to be active from and until given times
  Move carousel slides up and down in list
  More general move up/down table cells