Fix up group management, fix DHT node verification

validateKey() only works with Tox ID's of friends with nospam implemented. Since Tox Nodes don't have those, a separate function must be made.

Also, group management now looks like this:
![device-2014-04-13-014135](https://cloud.githubusercontent.com/assets/2215601/2688822/9716109e-c2ce-11e3-87e5-2b8edcdf661d.png)