AVRCP 1.6: media browsing support on Target(3/3)

Description:-
This patch provides Media browsing support for AVRCP using
new Media Browsing APIs provided from Android 5.0

Features:-
1) setAddressedPlayer
- Change the control to the specified player
2) setBrowsedPlayer
- Change the player with which fileSystem is being browsed
Browsing commands:
3) getFolderItems scope=MediaPlayers/VFS/NowPlaying
4) changePath
5) getItemAttributes
6) playItem
7) getTotalNumberOfItems

Handling notifications:-
1) ADDRESSED_PLAYER_CHANGED
2) AVAILABLE_PLAYERS_CHANGED
3) NOW_PLAYING_CONTENT_CHANGED

Added support for dual RC

New files added:-
AvrcpHelperClasses.java
- Helper classes used for callback/response of browsing commands.
AvrcpConstants.java
- Group all the constants used in Avrcp.
AddressedMediaPlayer.java
- Interface to communicate with media controller for NowPlayingItems.
BrowseMediaPlayer.java
- Interface to communicate with MediaPlayer for browsing FileSystem.
AvrcpMediaRspInterface.java
- Interface to communicate with the native layer.

Verification:-
AVRCP 1.5/1.6 functionality has been verified with
google MediaBrowserService sample app.

Bug: 19361366
Merged-In: I0ab7f0c7d87c06fe4f454151d20494c56aceae12
Change-Id: I40b9e7aae81d994a709559844928b0749c603ea8