proof improvements

[thevirtuoso1973]

• More consistent interface with build
• Don't rely on colour as much, since users may have their own term colour settings that won't match.
• Highlight image predicates.
• Option to omit resolution steps
• Collapse operator applications. e.g. cases like

  (
    (
      ...
    )::op1
  )::op2
  

• Nicer run formatting. Might need a different proof tree printer however. Ideally it would be 'newline aware', where it will correctly indent newlines.

[thevirtuoso1973]

Would be pretty useful to diff proof trees as a regression test method.
E.g. your CI/build system can print out tree diffs as a warning for any new commits.

Not sure how best to actually implement though. Could start with just a simple text differ and somehow integrate from there.