Don't enter edit mode when changing cell type and preserve renderd.
alt+enter should always insert below
shift+enter and ctrl+enter swapped.
Fixing help strings for shift|ctrl+enter.
Fixing tests from shift and ctrl enter swap.
Merge pull request #4916 from ellisonbg/modalbehavior

Fine tuning the behavior of the modal UI

swap back shift- and ctrl-enter, to their rightful places.