Refactor torrent.update_state
Replace pause_all with pause_session

 * Replace pause_all and resume_all with pause_session and resume_session
 * Pausing all the torrents individually loses the original paused status
   so use the libtorrent session pause instead.
 * Added a SessionPausedEvent to the method.
Clean up code for setting error state
[#1032] Error out torrent if data is missing on startup

 * Add fastresume_rejected_alert handler and force a Deluge Error state upon alert.
 * Retain original resume_data and prevent overwrite while in Deluge Error state.