I'm back to working on this.  I've made good progress: I'm nearly done with all of the changes suggested here and ready for another PR review.

I'd like some opinions on a few things:

1. Should the tooltip-related configuration options be removed?  There is one for whether to show tooltips for squeezed outputs and another to set the hover delay.  I feel that they add unnecessary complexity.

2. Should there be an option to entirely disable auto-squeezing?  Currently there is only a setting for the minimum number of lines, which can just be set very high.

3. Should we keep the events for squeezing the last output block and expanding the last squeezed output block?  ISTM the keyboard shortcuts would only be used by "power users", which aren't our main target.  Further, without keyboard shortcuts, I see no point for having these events at all, given that it is easy to achieve this otherwise.

4. Is it worth the effort to update the number of lines displayed for squeezed outputs when a shell window's width is changed?