Mention the filename and the driver error text (though this last thing
doesn't seem that useful). Also, don't spam with failures afterwards
when the database failed to open.
At the same time, fixed the order in the QuickOpen plugin to make sure
the RefreshInterval setting isn't immediately removed after saving it.
Also disabled debug output for settings database.
Potential replacement for QSettings. This database will allow us to save
settings incrementially, removing most of the performance issues we're
having when our few megabytes of settings are being saved.
Not done in the form of a QSettings backend because it doesn't seem the
backends can do an incremental update of the settings.
Currently used by the QuickOpenPlugin for testing.
