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
I leave this as CreateConference, since it would be not accurate to refer to it as "creating a conference call", since there is no such object at oFono level, only an array of calls in a conference at a given moment.