The applicationObserver was never unregistered resulting in a memory leak
and even worse, crashes when destroyed dialogs still got called through
the applicationOnVolumeChanged callback.
Also changed the view resource identifiers used by the controller dialog
as it used the same resource identifiers as the now playing panel.
* Allow the RemoteActivity and BaseMediaActivity to show a volume controller dialog when hardware volume keys are pressed
** The dialog handles the key events and makes callbacks to the activities to handle showing the dialog itself
* Minor improvements
** Make HighlightButton render in the IDE GUI Editor
** Minor code cleanup
** set currentActivePlayerId = -1; on playerOnStop in BaseMediaActivity to be more consistent
resolvesxbmc/Kore#235