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
Is this really a rule? For sid and hide it makes the code more readable and with a better flow (also easier to debug). Or do you prefer long and crowded code lines? The compiler will optimize it anyway.