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
how about
```
var output = (txt instanceof Object) ?
              '\n[Telephony JS] ' + toPrintableString(txt) :
              '\n[Telephony JS] Error: ' + txt;

console.log(output);
```