CB-6153 Add a preference for controlling hardware button audio stream (DefaultVolumeStream)

This, along with the commit to the audio plugin, makes it so that by
default apps control the ringer volume, but when any audio players are
active, the media volume is controlled.
CB-8112 Turn off mediaPlaybackRequiresUserGesture
Merge branch 'master' into 4.0.x (volume stream & setMediaPlaybackRequiresUserGesture)

Conflicts:
	framework/src/org/apache/cordova/CordovaActivity.java
	framework/src/org/apache/cordova/CordovaWebView.java