aula-init-state needs more power

[fisx]

we need to be able to call aula-init-state for extra tasks, selected via command line:

• whipe all existing data files, and the directories that contain data files, and create a fresh copy from the current release. this is needed to pull in data files that have been added / changed / removed w.r.t. last release.
• make content and make content-deleg do not work any more because of recent changes to aula.yaml. this should also be done by aula-init-state, with $AULA_URL from the Makefile a cli argument, so it can be called from abroad.

[fisx]

(I think it may be nice to use https://github.com/soenkehahn/getopt-generics for this, but only if it can do what i remember, rather than just the stuff that's described in the readme.)