Pin a cell to top of page so you can see results of edits when editing cells far up/down page.

[kalmdown]

At a certain point notebooks can become long and it becomes unwieldy to drag sets of cells near the frame that is being rendered.

I would like to pin the cell that is rendering what I care about to the top so I can keep it in view and make edits, run them and see the changes without scrolling, often losing my place, and likely missing an aspect of the redraw that will help me debug.

[mootari]

See also #52