Make SMS callback handler also handle status-updates / callbacks in addition to inbounds / replies

The callback url - Ex: http://www.example.com/sites/all/modules/civicrm/extern/sms.php only handles inbound / replies at the moment, and doesn't do status updates / callbacks.

Parameters during a callback are : apiMsgId, cliMsgId, to, timestamp, from, status and charge.

Presence of status parameter for example should be enough to determine that its a callback and should be forwarded to callback method of CRM/SMS/Provider/Clickatell.php. Flow goes to inbound() otherwise.