router.js: improve usability for devs

- [ ] 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.

Start by reading router.js and mapping the existing route helpers, their dependencies, and static route segments. Done means helpers are grouped by required dependencies, camp-dependent route names consistently begin with camp, and any adopted static segments are exported constants with usages easy to locate.

Written by the indexing model from the issue text.