router.js: improve usability for devs

[BacLuc]

• the helpers should be organized along their dependencies. (all routes that need a camp should be in campRouteHelper, all routes that need a materialList should be in materialListHelper).
• all routes which need a camp should have camp at the start of their route name, independent if they are a child page of /camp or not.
• Maybe use exportable constants for the static parts of a route, that we can change the content of the static part, we see the usages without ctrl+f, and also see if something is unused.