Restore connection caching

- Connection caching does in fact work, and that's how the legacy
  discuss code worked.
Call check_update() before load_info()

- We must call mtg.check_update() before load_info() to
  correctly determine whether the meeting exists or not.
  Because legacy code.
Catch NO_SUCH_TRN when looking for the next transaction
Remove weird socket.error catching
Clean up UI for errors when parsing meetings.