Support for color widget

Issue for UIP2: ✨ Support for color widget Active

I also put changes from the MR of ✨ Support for color widget Active . But finally it is not needed.

- Only one prop type, with transparency optional.
- Add convert_from
- alter source plugin definition to allow textfield widget

I created another MR to have ✨ Support for color widget Active and ✨ Prop source to get background URL Active appliable as patch.

Thanks! I will add a followup ticket to make it configurable with ui patterns ui.

It seems that this had never been merged.

grimreaper → closed merge request !42

MR rebased.

Patch for Composer.