Allow view to keep rotating while other tools are used

[Carifio24]

This PR resolves #334. I think the most straightforward way to do this is to have the rotation tool not be a CheckableTool, but instead just be a Tool which internally tracks whether it's currently rotating or not. We also got a request for this functionality recently.

Since this a frontend-agnostic tool, there isn't way to do something like update the icon without creating frontend-specific subclasses, which feels like overkill to me when the tooltip pretty clearly states the button function.