Allow expired events in the grid and style with phonecian purple

[dch]

This does what I want, but likely needs a solution to allow the expired events to be removed gracefully at some point from the dashboard.

I'm not sure what that would look like, so here's enough of a patch to spark the discussion.

[ghost]

Works for me! I wanted to avoid giving people the impression this was reliable, though, in the sense that if you open up the dashboard, you're never going to see expired events that happened before you arrived--expired means riemann no longer knows anything about them. ;-) With that in mind, it probably makes sense to use this visual cue once, then fade out the event after a few seconds.