[ninsbl]

I have been experiencing issues with SQLite connections like "Locked database" when registering maps in relatively large STDS. This PR is an attempt to make connections a bit more robust by:

1. adding a busy_timeout: operations do not fail immediately if a lock exists but wait at least 30 seconds.
2. putting all PRAGMA definitions for the connection in one script and execute it with connection.executescript(). When connection PRAGMA was set for SQLite with connection.execute(), a result row was lingering. executescript does not leave that result row lingering.
3. execute_transaction was supposed to wrap an SQL statement with BEGIN and END. However, the initial, and not the wraped SQL statement was finally executed. This is fixed here as well.