Added beginPlayback function

And implemented it for html5
Also made HTML5 stop function reset to the start of the media as well as pausing
Merge remote-tracking branch 'origin/master' into new-media-api-beginplayback-spike
Add beginPlayback function for CEHTML
beginPlayback implementation for samsung
Improve doc comments for beginPlayback
Added common test for begin playback from stopped state
Add common tests for beginPlayback from other states
Added Samsung Maple test to ensure device Play is called when calling beginPlayback
Add beginPlayback test for HTML5 implementation
Test for CEHTML beginPlayback