Epics and features layout: integrate ideas categories

In the ideas, we categorize them to easily filter or spot ideas of the same topic/area.

when you are making your strategy and want to know "what are the planned changes on our category a" you could easily filter for it.

At the moment we can only use custom fields, but this means, they are copies of the categories of ideas. This invites error.
The exact same categories of ideas should be available in Epics and Features, so that it's easy to filter there for the same topic, too.