MediaScanner: Do separate bulk inserts for different media types

This should fix a bunch of problems introduced in the original bulk insert implementation

Also reverted two changes that are no longer necessary:

Revert "MediaScanner: Add virtual NO_MEDIA column to fix support for .nomedia files"

This reverts commit 92e1314a.

Revert "MediaScanner: fix breakage in updates"

This reverts commit 45aaa2a3.

Change-Id: Ibed66393467761c2c1ce48deb09bcac505b7d221