[BUG] Removing track should switch selection to nearest neighbor, not 0.

[subdavis]

UX bug.

"This is very time consuming to have to scroll back down to the detection number we left off at"

[subdavis]

Also, inserts should be sliced into the track list right after the current selected track if one exists, not allowed to appear anywhere in the current frame's time window. This will require a bit more thought because we're only sorting by frame. There's no ordering within frames.