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
move declaration of found into loop. And I'd like to rewrite the part logic in loop as below
```
TelephonyService* service = FindService(p);
bool found = !!service;
if (!service)
  service = new TelephonyService(this);

bool ret = service->Init(p, props);
if (!found && ret)
   services_.push_back(service);
if (!found && !ret)
   delete service;
```