Moved DBConnectionProvider to Database component

This is blocking independence of other components and is thus high prio.
Namespace should be fixed in a follow up refactor.

Change-Id: I43d3fabce4b25fb89b683c30edc4a873fcebdce4
Get rid of MW dependency in QueryEngine component tests

Change-Id: I90187c585b6c84922e5f096aad87d6047f6f3300