Add possibility to fold some regions in model/view tabs

[Dumluregn]

Inspecting the editor with a lot of contents (or simply a medium sized table) isn't super fun, you need to scroll a lot to find a place that you need. It would be helpful to allow folding and unfolding the particular elements, similar to the browser DOM inspector.

The UI could also be similar - adding a small arrow before the element which should fold/unfold it, and clicking the element name itself should work as it does now.