Fix offline mode and make it a bit more user friendly

Fix offline mode and make it a bit more user friendly

Hopefully, there are not many new bugs :)
The notable changes in submodules are:

Submodule coffee-flask 9b74ccb..d99857c:
  > Center all content
  > Show current content of the offline queue when going offline
  > Do not allow multiple reconnect timers running simultaneously
  > When replaying offline queue, use the original event time rather than now()
  > Remove unused variable
  > Replace "fuck" with "ajax_failure"
  > Logout automatically even without selecting any beverage
  > Implement clean switching between online and offline mode
  > Catch all exceptions in JS function updateUI
  > Use new data structure for offline-collected data
  > Remove commented out code

Submodule terminal/src/mt-apps 89b7898..8a4c5fe:
  > Make it easier to call showOfflineQueue() from remote scripts
  > Replace tabs with spaces
  > Do not generate "empty" messages
  > Rework offline mode
  > Store offline data in an array rather than in a hash
  > Use more distinguishable user ids for simulated users
  > Replace tabs with spaces