[FEATURE] widget groups

__Requires:__
https://github.com/sulu-cmf/SuluAdminBundle/pull/164

__Tasks:__

- [x] make widget-groups configurable
- [x] remove the hardcoded contact-routes
- [x] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | https://github.com/sulu-cmf/docs/blob/master/detail-specification/100-basic/DET-106-Widgets.md#widget-toolbar