Gallery2: support stereo/single track play mode

(cherry picked new files from commit id
990c6d43ea7c184846e19d41bef0d93aee4e581b)

Change-Id: I2d7d523ca586a031c3fb139eda321d5073b30589
Gallery2: support stereo/single track play mode

User can select stereo/single track play mode.

Change-Id: I8225739815484f3c288823802f68478cb457725e