Expanded volume panel with sliders and mute buttons.

Bug: 3395734

Volume panel that can be expanded and can be used
to control different streams' volume and toggle
silent mode.

Shows the active stream's slider on top and the
remaining below. Touching outside dismisses the
dialog as well as a 3 second timeout.

Dialog fades out after timeout.

Change-Id: Ief258cc904bfd3d62f1291adba4a9cf442bcb006