Fields and forms redesign

The tab *Fields* on the vector layer properties dialog should be split into two different tabs that separate data-related from form- and widget-related user interface elements.

This is expected to improve user experience and usability.
Yes, exactly.
Actually, I wonder if it would not be better to just throw them all into one single tree widget.
Collapsible group boxes IMO mainly make sense when you have a mix of different widgets which you want to group (more complex than a simple list). But that would also apply to the toolbox (the one in the mockups). A tree widget is perfectly fine for bringing structure into lists.