replaced reflections from bundles action with configuration in admin

This PR changes the way the javascript from the bundles is included. From now on there have to be a getJsBundleName function returning the correct folder for loading the main javascript file (e.g. `sulucontact` for /bundles/sulucontact/js/main.js, the part around sulucontact is generated) /cc @sulu-cmf/developer 

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | https://github.com/sulu-cmf/docs/blob/master/developer-documentation/000-foundation/admin-integration.md