[horhulenko]

Resolves #665

The grouping content window doesn't block HAL anymore. You can open several and keep using the graph.

About the concerns in the issue:

• too many events: each one has a simple answer

  event	window
  rename, recolor	updates the title or the color box
  items added or removed	rebuilds the tree once, after the changes stop
  grouping deleted, netlist closed	closes
  Python script running	waits for it to end, then rebuilds once

• big effort: ~150 lines. HAL has ~276k lines of C++, so this is about 0.05% of it, nothing in core

• expensive: it isn't

	this PR	rebuild on every change
1000 changes	1.8ms	650ms
10000 changes	5.3ms	45s

A script assigning 20000 gates takes the same time with the window open or closed. 50 open windows add 0.25µs to each unrelated change.

Tests.zip. All 59 checks pass.