Add 2 APIs (suspend/resume) in MediaPlayer

- API:suspend() will just pause the player and release all the decoders
  to replace release() which will release the whole player
- API:resume() will just init the decoders again,
  then start() will be called to restart streaming playback
- Add a check in AwesomePlayer::onVideoEvent()
  to make sure the first seek operation will always seek to the next
  i-frame

Change-Id: Ie4c82906a2a056378119921a656128ebdc1007c4