ExoPlayer v2

Upgrades to ExoPlayer2 and redesigns the public Api.

Notable api changes:

• Players are created via PlayerBuilder instead of PlayerFactory
• Listeners are attached via Player.getListeners().add... instead of Player.add...
• Player.reset is removed in favour of Player.stop

PRs:
#17 Barebones ExoPlayer2 migration (without drm/subtitles)
#21 Refactoring exoplayer facade listeners
#23 Refactoring exoplayer forwarders
#24 Refactoring media player listens
#25 Adding audio tracks to exoplayer
#26 Avoid leaking exoplayer classes to public api
#27 ExoplayerImpl and ExoPlayerAudioTrackSelector unit tests
#29 Demo audio track selection
#30 Adds ListenerHolder collaborator
#33 MediaPlayer facade tests
#37 AndroidMediaSelector tests
#38 Mediaplayer facade refactor/tests
#39 Consistent reset logic
#41 MediaPlayer state exceptions
#42 Reducing listeners scope
#43 MediaPlayerImpl creation refactoring
#44 decouple exoplayer constructor listeners
#45 Removing notils
#47 Readding subtitles
#48 Widevine modular streaming support
#50 Widevine modular download support
#51 Drm error propagation
#52 Exposing non secure decoder usage as client api
#54 Asserting Drm is supported when attempting to use drm
#55 Package restructuring
#56 Wrapping exoplayer TextCues to avoid leaking
#57 Replacing PlayerFactory with PlayerBuilder
#58 Javadoc supported public api
#59 Introducing internal package for all non support public classes
#61 Fixing NPE in subitles
#62 No longer exposing PlayerChecker in favour of more information on PlayerInformation
#63 Removing leaking Player from error listeners
#64 Removing Typed player errors and instead providing a ErrorType
#65 Delegating SurfaceHolder lifecycle to exoplayer
#66 Decouple error messages
#67 Fixing exoplayer surfaceholder usage