[qtcontacts-sqlite] Return self contact if explicitly requested by ID

Filter out of results otherwise.
[qtcontacts-sqlite] Ensure notifications are emitted after commit

If the transaction is not yet committed, the notified updates are not
yet visible to other processes.
[qtcontacts-sqlite] Fix signal propagation
Merge pull request #3 from matthewvogt/txn-fix

Ensure that transactions are complete before emitting notifications