Check what is going to happen with TGN and if down forever, remove from this skosprovider

[Jonas Geuens]

The TGN endpoint has been down for time: http://vocab.getty.edu/tgn

If this downtime continues and Getty has no intention of bringing the endpoint back online, we should remove the endpoint from the skosprovider.

[Koen Van Daele]

Looks like it needs a trailing slash: http://vocab.getty.edu/tgn/