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
For the declare var as close as first used, yes it is from google C++ coding style doc: http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Local_Variables, please follow.

For the avoiding used-once variable like `sid` and `hide`, it depends on you.