added highlights to scrubbable numbers on hover and on (alt+shift)-keydown and changed mouse pointer on cmd/ctrl-down

- activated pointer events for cm-number spans
- added a style for cm-number:hover to highlight number which can be scrubbed
- adding same style as a CodeMirror highlight on (alt+shift)-keydown if a number is under the text-cursor to indicate it can be nudged
- when cmd/ctrl is pressed while hovering over a number the cursor is changed to a col-resize (left-right-arrow) cursor to indicate that user can now start dragging and which direction to drag to