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
Yes, after the PR is integrated, these steps are needed. The packages needed to _run_ this are already there. The recommended packages needed to _test_ it are described above. What I was not sure about is where to put this info. If it's fine in the readme, let them be there. Or did you mean that I could remove some of those comments and steps, and leaving others?