Move all of the reasonable DatabaseBase methods to Database class

Move all of the reasonable DatabaseBase methods to Database class

The Database class was previously just a short-hand for "Database::",
and such calls should still work. The class now resides in /libs/rdbms.

The subclasses now extend DatabaseBase to avoid breaking type hints
that use that (hints use either IDatabase or DatabaseBase).

Also, use CASCADE with DROP TABLE for MySQL as with other DBs.
Keep SQLite excempt due to lack of support.

Added getDomainID() methods to avoid mentioning the word "wiki".

Change-Id: Ibd05d786cb26c21dcc9cb9601f6b2b52056af9ae