GROUPS: A way to pin topics in order at the 'top' of a group

[BeccaMelhuish]

What is the problem?
Ideally, Story of Estonia would need to be able to pin the 6 topics in their group in order, as the topics will each have a question, which are intended to be answered in order.

Why is this a problem?
Sometimes the order of the topics is important. I have seen other use cases where this is relevant too - like consultations with several topics with different themes.

Possible solution.
Can we offer a feature to 'pin' topics in a certain order?

@ilmartyrk let's discuss what is technically feasible to make work by mid March (with user testing before then), then see if we need a design yet :)

[BeccaMelhuish]

Ilmar/Viktor: Could be draggable, like vote option dragging.
Initial estimate: 3 days.
But drop for now, due to this (once fixed to order by last edit, admin can 'hack' this. Not ideal but works for now): #1786