Media scanner support for tracking files of arbitrary type.

The native media scanner no longer filters files based on file extension.
Audio, video, image and playlist files are handled as before, but non-media
files are now inserted into the "files" table, which was originally added
to support MTP.

Change-Id: I9053218fb6d2671a3bb181405c34442b94678afc
Signed-off-by: Mike Lockwood <lockwood@android.com>