[WIP] Add initial support for creating schema

[eneufeld]

[koegel]

I like the idea but I would not add it for the upcoming demo.

[koegel]

Open Issues:

• I need to be able to name the new property at least initially.
• What about adding nested properties?
• Maybe moving the creation into the Control tree would be better so nested properties could be addressed, e.g. + button on each object including root, an then dialogs to select type and name.

[sdirix]

Thanks for the PR! I like the concept!

I found an issue: Creating a control within a detail form fails.