Only have focus if multiple views

[garrettjstevens]

I wanted to see how #3860 might feel. You can try it out here: https://s3.amazonaws.com/jbrowse.org/code/jb2/3860_focus_only_multiple_views/index.html

[carolinebridge]

This feels pretty good imo -- the context when you add a new view and click around (thus enabling the light/dark relationship) feels like enough to communicate the concept of focus to the user.

[cmdcolin]

another way to make it more abundantly clear which is active is to put e.g. "(active)" in the title bar if there are multiple views

I almost think making the color hint subtler and adding that could be useful. alternatively the border concept could be reconsidered but i'd just try to avoid something like a yellow border as it is a little bold...just a subtle border i think would be nice. as i'm typing in this textfield for example, there is a little blue border that turns greay when i click away

[cmdcolin]

I would not make it so that the focusedView getter returns undefined if there is only one view, because focusedView can be used for other purposes (keyboard shortcuts)

[cmdcolin]

Whether we want the color to change only when there are multiple views, or to return the actual view instead of the id, may be separate issues. I think id is not bad as it is easier to convert to a persistent model attribute

[cmdcolin]

as mentioned in my above comments, this approach will likely be unused. I will vote for close (sorry, just trying to close out old PRs). we can re-visit if this is of interest still in a new pr