Implemented the metadata changed notification filters.

IMediaPlayer:
new setMetadataFilter method so set a filter (2 lists of allowed and blocked metadata type)
serialized in a Parcel.

MediaPlayer.java/android_media_MediaPlayer.cpp/mediaplayer.cpp
new setMetadataFilter that passes the filter down to the MediaPlayerService's binder interface.

MediaPlayerService.cpp
The Client inner class holds the allowed and blocked metadata types.
These are in 2 vectors that get populated in the setMetadataFilter.

A new shourldDropMetadata method returns true if a type of metadata should be dropped according
to the filters.

The notify method in run the metadata update notifications thru the filter and possibly drop them.