Clean up “features” config block

[fm3]

The application.conf block called “features” is exposed ot the front-end. It does not yet follow the conventions introduced in #5208. Also, it could be argued that it does not semantically represent features anymore.

Idea: distribute its contents to where they make sense semantically, annotate in wkConf which keys should be propagated to the front-end.

Features route could be renamed to /api/webknossosConfig to avoid the mismatching “features” name