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
looks a bit messy... it is nicer with returns if possible... wish we could do local methods like js and python... not sure if c++11 lambda makes that possible