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 can just delete pointers in destructor without erasing, as container will take care of that when out of scope.
i.e. `for (auto i : services_) delete i;`