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
After trying it, no, it becomes much less object oriented after that. It also looks more ugly. So it remains with classes. Now changing the member names is OK, but changing to private and accessors defeats the purpose of short, readable and maintainable code. Typical case of shooting with tanks on mosquitos. These are local classes... The code style makes sense for public classes, but for small local helper classes this is overengineering and should have exception.