v2: Have in-place toolbar

[jdittrich]

Story: As a user I want to have easy, visible/UI functions to manipulate objects and/or set their properties

Solution: Have a toolbar with widgets that allow to change things on the object.

Details:

• toolbar should/could be placed at the element itself
• draw2D does do UI with jQueryish statemanagement, maybe we want something more sustainable

[AlaaSarhan]

did some POC on this in branch 55-add-element-toolbar .. so far it implements basic only button element options.

I'm going to push this back to prio work on the more preliminary prototyping we talked about in milestones