Add back-end interface to get menu information for stacks of a project
Retrieve stack menu info when needed instead of caching

In three spots, the stack menu information for the current project was
needed. Up to now cached information was used to get this data. This
commit changes those spots to request the stack info right when needed.
This simplifies the code a bit as the cache doesn't need to be kept up
to date anymore.
Remove not-needed project- and stack-data cache

This cache is not used anymore and can therefore safely be removed.
SVGOverlay: connector arrows are now cached.
Caching avoids removing and inserting into the DOM, an expensive operation.
Merge remote-tracking branch 'origin/remove-project-data-cache'

Conflicts:
	django/applications/catmaid/static/init.js