[Package] Implementation of Tizen Package API

This branch includes a fully functional implementation of Tizen Package API. 

API specification can be found at:
https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/package.html

BUG=XWALK-443
`ret` seems no need to be clared, how about
```
if (package_manager_unset_event_cb(manager_) != PACKAGE_MANAGER_ERROR_NONE)
  return CreateResultMessage(WebApiAPIErrors::UNKNOWN_ERR);
```