IGGraphEditor: limit aspect ratio (or "narrowness") of editor

[szhorvat]

When launching IGGraphEditor with a path graph, it produces a very narrow display that:

• is difficult to work with
• cuts off labels

We should think about how to improve this. Of course dragging vertices outside the frame extends the frame, but it might still be a good idea to set limits of the minimum height / width.

[kubaPod]

If the initial range's aspect ratio will exceed a limit (10) then the range will be 'squared':