snap group to grid if SHIFT is down or "always snap to grid" is enabled #229
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This PR addresses #198.
Problem
Groups do not snap like nodes do, which makes maintaining neatly aligned nodes extremely difficult/cumbersome.
Solution
Make groups behave like nodes, by snapping their position and size to the grid:
demo.mp4
When "always snap to grid" is off, holding SHIFT enables snapping for groups, as is the behavior for nodes.
Snapping also works when pressing CTRL while dragging a group to release the "tether" from the group to its nodes.