This gets rid of the csync_statedb sqlite layer and use
the same code and same connection as the rest of the SyncEngine.
Missing functions are added to SyncJournalDb and change a few minor
things (like changing SyncJournalFileRecord::_modtime to be an int64
instead of a QDateTime, like it was in csync).
The current implementation would return the same value whether the query failed
or if no row would be found. This is something that is currently checked by csync
and needs to be provided if we want to use SyncJournalDB there.
Adjusted all call sites to also check the return value even though they
could still just rely on rec.isValid(), but makes it more explicit as to what
happens for database errors in those cases, if we ever want to gracefully handle
them.
