selectablemixer: Add audiomixerbin

Change-Id: Ib82b80baaf630424da28a8e1c990f0f5bbc1c5c1
selectablemixer: Connect audio inputs to the audiomixerbin

Change-Id: Id04fdbc9de9e35e123971f68272aca4da9b1b0b4
selectablemixer: Manage disconnection of audio streams

Change-Id: Iaa3a51792f7364af4bc39d9984980b36ce052df7