Layout visible cells are hidden when cut and pasted.

[nitind]

Issue https://github.com/jupyter-incubator/dashboards/issues/202 saw us remove the layout information on cells that were copied to the clipboard, so that when pasted, they didn't result in duplicated layout information requiring manual correction by the user. The notebook's cut_cell function, though, is literally calling the copy and delete functions rather than doing something unique, so is also affected by that change. Find a way to retain the layout information during a cut and still avoid duplicating it during a paste.