[Timeline] non-focused image snaps down to center of screen when focused

[AudreyBeard]

Timeline focus updates earlier in scroll, but it snaps the now-foregrounded image down to the center. Seems to require:

- update timeline-focus-update position relative to screen (as opposed to # of pixels)
- not snap image

I haven't dug into the code here, so I could take a stab at it later.