IDs instead of hyperlinks for model relations

[dkellner]

As discussed yesterday we remove hyperlinks for displaying model relations in favor of plain IDs. There are mainly two reasons for this:

• The frontend will hardcode at least the quest categories' ids to attach custom styles to them. URL make this more cumbersome than necessary.
• Using URLs instead of IDs makes it harder to move the backend to another domain, which will actually happen soon (#15).

@normade If you're fine with this, you can merge and deploy it already. @Twissi is waiting for it, afaik :-).