RFE: Mouse modes snapshots or undo stack

[Zach Pearson]

When using the segmentation tool, the user can set a preference to set mouse modes automatically. This makes the tool save all current mousemodes, then override them with its own modes, and then on close restore the previous modes.

To accomplish this, it uses its own ad-hoc dictionary of dictionaries: each mouse button is a key to the top level dictionary. On the second level the keys are modifier buttons and the values are mouse modes.

It's not that this solution doesn't work, it's just that if some other developers want to make their tools do something similar then they'll have to implement some code that duplicates mine and if some user happens to use two of those tools at the same time it'll cause havoc. It would be good to centralize this behavior if we see another developer talking about automatic mouse modes on the mailing list so ChimeraX can track which mouse modes to save and restore, rather than individual bundles which may clash.