Markdown field toolbar misplaced when parent list item is reordered

[erquhart]

When re-ordering a list item that contains a markdown field, the toolbar ends up in the middle of the field, or missing entirely, until a scroll takes place. The sticky toolbar resets its position when different events occur, we just need to make that happen when an ancestor list item is reordered.

[erquhart]

position: sticky is in all of the browsers we support it seems, so we might able to swap the toolbar sticky code out entirely.

[erquhart]

Went with position: sticky in 1.0.