OfflineGuidesActivity: Require login

Otherwise it crashes.
OfflineGuidesActivity: Add loading indicator
Sync: Flip update progress check

The logic to determine whether or not to update progress in the DB was
backwards because we _do_ want to update progress for a manual sync
because the user will likely be viewing the offline guides list looking
at progress.
Return offline guides in insertion order

This makes it so the most recently favorited guide is displayed at the
top.
Syncing: More robust error handling

This handles connection errors, auth errors, and other general problems
that arise and takes the appropriate actions for the sync status for the
system and the notification displayed.