Visualize individual trace choices when curve is "selected"

[zane]

If you select (through some mechanism TBD) a curve the visualization should enter a state where it is focusing on that trace. When in that state:

1. That curve is made more prominent somehow relative to the other traces. (Perhaps by raising its opacity and lowering the other curves' opacities.)
2. The color the points should be based only on the choices made by that particular trace.

This will help us debug "strange" curves.