CB-8031 Fix race condition that shows as ConcurrentModificationException

Conflicts:

	framework/src/org/apache/cordova/PluginManager.java
CB-8081 Allow gradle builds to use Java 6 instead of requiring 7
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.