Allow nodes to be "grouped"

It would be very useful to be able to create "groups" of nodes. The main idea would be to have the ability to lasso a set of nodes, and/or draw a box surrounding nodes, and have them treated as a unit in terms of layout, etc.

This would let you take large diagrams and organize them much more effectively. It's not so much of an issue when there are 10 nodes, but with 100, being able to say "this section of my diagram related to Foo" and "this section relates to Bar", in a clear and meaningful way, would be helpful.

The key functionality to make this very usable would be to allow:

1. Lasso or box around a set of modules, causing them to be "grouped"
2. Make layout methods layout within a group, but then move/arrange the entire group as a single unit (ie: don't move an object within a group away from the group itself)
3. Have some visual clue as to where your groups are
4. (Optional, but nice) Select and move a group as an entirety

For example, I've attached an image showing the "Layout and Pathfinding Algorithms" sample with a visual example showing how I'd envision this.