Filter TUI to just the ancestry and descendents of the cursor on Spacebar

[whereswaldon]

This seems like it would be really useful as a toggle. Hit spacebar once to hide all extraneous messages (relative to the selected one) and then again to return to the normal view.

I think it would be especially useful if you could still scroll the cursor while in this filtered view, and dropping out of the filtered view would keep your cursor on the message you had selected in the filtered view. This would let you use the filter as a way to scroll faster through time than the normal scrolling mechanisms.