[FEATURE] implemented functionallity needed for widgets in the sidebar

__Tasks:__

- [x] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | No because of the dependency to the core bundle - needs to be merged before
| Fixed tickets | -
| BC Breaks     | -
| Doc           | -

__Requires:__
- https://github.com/sulu-cmf/SuluSalesCoreBundle/pull/7
docu is missing