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

Add tools/hands-audio to build and update .gitignore
handsfree-audio: Add Alsa dependancy

Alsa will be used in order to playback sound received over SCO.
handsfree-audio: Implement alsa playback
handsfree-audio: Add SBC dependency

mSBC codec is used in HFP 1.6 Wideband Speech.
handsfree-audio: mSBC support
handsfree-audio: Add USR1 signal to connect audio