Keep the user's input form open in case a term does not typecheck.
Remove any selections in a proof on a click outside the proof's container node.
Make simplified selection the default.
Change highlighting of steps for selection and hover, lighten highlighting of hovered exprs.
Move the Save/Restore button from the step editor into the proof editor.
It displays now above the proof and always displayed in editors.
Fix the step and expr selection logic in the UI, adjust shade of hover highlights.