Perform a sanity check on database at launch

[barijaona]

Run sqlite's PRAGMA quick_check on app startup. Vienna will advise user to restart from a good backup if possible.

If this is not possible, I got a decent result by running the following commands in Terminal:

mv messages.db corrupt.db
sqlite3 corrupt.db ".recover" | sqlite3 messages.db

[Eitot]

It would probably good to create a section in the help book and add a "help" button to the alert so that users can find out what to do.

[barijaona]

It would probably good to create a section in the help book and add a "help" button to the alert so that users can find out what to do.

The FAQ section of the help book needs some reorganization. Will add this subject into it.