Add "staging closed x seconds ago" to the staging screen

[samjmartin04]

Currently the staging screen counts down "0:05" for 5 seconds less before staging closes and then changes to "closed" when staging closes. It may be useful to have "staging closed x seconds ago" on the screen to either give the marshals/badgers some discretion over letting in a team that is only a few seconds late and/or being able to tell teams that they are too late.