Added native share dialog

Test code:

```
facebookConnectPlugin.showDialog( { method: "share_open_graph", href: "http://test.com" }, 
                    function (response) { alert(JSON.stringify(response)) },
                    function (response) { alert(JSON.stringify(response)) });
```
and
```
facebookConnectPlugin.showDialog( { method: "share", href: "http://test.com" }, 
                    function (response) { alert(JSON.stringify(response)) },
                    function (response) { alert(JSON.stringify(response)) });
```