Add buttons to jump to metacategory

When there are many categories it would be useful to have something like a jump button so that users don't have to scroll as much.

changed the description

In particular I think that a sidebar (visible on bigger devices and conditionally displayed on tablets / mobile phones) would a good solution for this. Design-wise I think something like this could fit:

I think in general it would be nice to make the meta category system more flexible e.g. allow an arbitrary (or max n) number of meta categories. This could then also be nicely integrated into the new sidebar.

@rveres did I understood it correctly that you wanted to give this a try?

Sure, I could try this on the weekend. Otherwise I try to do #188 (closed) again.

Sounds good!

assigned to @rveres

unassigned @rveres

assigned to @georye