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
Common issues
1. put member into private, if need getter declare `var_name()`, if need settter, declare `set_var_name()`, both put in header as inline.
2. naming: remoteParty - > remote_party