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
Sorry, no problem here, I thought it was in destructor. Well, you can use `++iter` to have better performance, it is not compulsory though.