Revised I/O Colouring

• Revised I/O Colouring:
  • Merge the previous modal and redfront options, and replace the I/O Colouring submenu of RadioMenuItems with a single CheckMenuItem.
  • Run-REDUCE no longer colours echoed file input.
  • I/O Colouring and Typeset Maths now operate independently and consistently.
  • The default colours for symbolic mode input and output are now green and brown respectively.
  • A new Font Colours dialogue allows you to customise the colours.
• Copy some redfront code into rrprint and no longer use the redfront package.
• Display a matrix assignment as an assignment in all output modes, but skip any intermediate assignments, as in plain text output.
• If you edit a command label but don’t confirm the edit, it will be saved anyway. (This was the behaviour in v2.2, which I removed inadvertently in v2.3 but have now reinstated.)
• The Hide Editor button switches focus to the I/O pane or input editor as appropriate.
• Fix vertical spacing of Typeset Maths output.