Add more return types to Database class

Add more return types to Database class

We expect these to be implemented and where
implemented we expect them to return these types.

This means when typehinting against Database
(Which is done throughout the code as we dont know
what DB we will eb using) warnings about void return
types will no longer be shown by static analysis stuff

Change-Id: I03d85560d9eb92d6df11dba8bc90339bf41cee8c