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
you disconnect, that makes the request, the MW replies first with the disconnect reason (change), then a state change (disconnected), then with a 'call removed' signal;