Add split name

Implements #25 (closed).

Currently the django branch is the target branch as otherwise all Django changes are visible as well. Proper MR will have staging as target when django is merged.

Works by assigning each split a name that has a comma separated syntax: a > b > c is equivalent to: subtask c in subtask b of task a (We can also use a different delimiter such as , or / if you prefer this). Out of this data a hierarchical table of contents is built on the client and subsequently rendered. This branch also adds jumpTargets / URLs to each answer-section (answers already have permalinks). Admins can change names and the toc is rerendered without fetching the splits again from the server. The toc panel can be hidden.

There are no visible changes for non-admin users unless a single split has a non-zero name.

Design is WIP - I am open to suggestions.

I am not sure if we want to merge this into django, waiting until django is merged is probably a better idea.