Time slicing

[jameshadfield]

Watching people interact with auspice has made it apparent that branches which are not in the selection (time slice, filters etc) are confusing to people. We currently draw them thinner, but they are still there, with on-hover info boxes etc. This PR improves the visual distinction between in-selection and out-of-selection branches / tips, especially for time slices.

• on-hover info boxes no longer appear for out-of-selection branches / tips
• There is no longer the ability to click on out-of-selection branches (and the cursor no longer implies this ability)
• out-of-selection branches are now thinner
• for rectangular layouts & temporal trees there is a grey background indicating the selected time slice. This looks especially good for animations and generally improves clarity (in my opinion).
  • Note that a bunch of tips & parts-of-branches are rendered as "in-selection" but out of this grey-time-slice... this is issue tree branch visibility is incorrect #473, those tips are actually out of the current selection.

[trvrb]

I think this is a significant improvement. Really nice idea.

I couldn't break anything. Please go ahead and merge.