Frame View UI Enhancements

[mmmaaatttttt]

Per Eli's feedback:

Right now on the preview page we can see all of the frames. Some enhancements:

• Don't show these all by default, hide them behind some kind of edit button (in general this page is too long now)
• When we delete a frame, have it transition out rather than being removed immediately. (Right now it's not always clear that you've deleted a frame)
• If we keep the left / right scroll, the active frame should stay centered if you use the arrow buttons up above