W3C Telephony API implementation.

Implements the latest W3C Telephony API specification found at http://telephony.sysapps.org/
Requires the oFono telephony middleware and the BlueZ Bluetooth middleware for working with paired phones.

BUG=XWALK-1419
Another question: if I make a container as a private var, with accessors, can I return a reference (see e.g. TelephonyCall::participants ) in order to have access to the container functionality, or have to hide and map out every used functionality?