snap group to grid if SHIFT is down or "always snap to grid" is enabled

[choey]

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.

[choey]

Groups would benefit from some sort of guide lines (like in #228), but that could be a future iteration. Some options to consider:

1. show guide lines orthogonal to the group (i.e., 2 horizontal and 2 vertical lines like it's done for nodes in show guide lines/boxes for nodes #228)
2. show guide lines for all nodes within the group

Maybe both?

[pythongosssss]

Hey, I apologise for the slowness, I think this functionality has since been added to core ComfyUI

[Latentnaut]

As far I remember, before the new interface, snap to grid ON behaviour was always snap, no need of press Shift.

That was super easy to aligh and tidy up nodes. With this Shift change, I always select two or three nodes accidentaly and it's tedious.

Any chance to come back to the original snapping behaviour?