Android: Make it possible for MediaPlayer to read from assets.

The Android MediaPlayer doesn't handle assets automatically, so we need to
open it and pass it in as a file descriptor.

Task-number: QTBUG-31422
Change-Id: Ic29c0ab6348d760cf21aa89ae423d41e15523976
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Android: removed unnecessary init class for QtMultimedia.jar

Change-Id: Ib13597389a3896da8b619993d197623e7c74a7e0
Reviewed-by: Christian Stromme <christian.stromme@digia.com>