handsfree-audio: Initial DBUS code

This code can register an handsfree audio agent and receive NewConnection and
Release calls.
handsfree-audio: Build handsfree-audio command line tool
handsfree-audio: Update .gitignore
handsfree-audio: Add Alsa dependancy
handsfree-audio: Link tool with Alsa
handsfree-audio: Allow connection without oFono
handsfree-audio: Implement alsa playback
handsfree-audio: Add SBC dependency
handsfree-audio: Link tool with SBC library
handsfree-audio: mSBC support
handsfree-audio: Add an option to kill incoming connections
handsfree-audio: Add USR1 signal to connect audio