Fix some SQL error and warning

Such as:
 Error opening the db:  "Driver not loaded Driver not loaded"
or
 QSqlDatabasePrivate::removeDatabase: connection '...' is still in use, all queries will cease to wor

We need to clear the QSqlDatabase _db handle before calling removeDatabase.
And we also need to give a different name to different folder database, just to be sure
Fix mutex usage in the journal

All public function must lock the mutex. And therefore none of the journal
function may call public function because the mutex is already locked.

So have a public commit that lock the mutex,  and a private  commitInternal
that assume the mutex is locked