Improvement: coloring improvements, and remove `echo-error`

[balupton]

I won't have time for this, however I would welcome someone to do a PR for it.

• [ ] ensure all background and foreground color combinations are suitable for color-blind people
• [ ] check if there are styles being invoked that are missing
  • [ ] perhaps echo-style can write to a $DOROTHY/state/warnings.txt file, that is dumped when new terminals are open; this can also be used for deprecations
• [ ] provide good2, notice2, neutral2, error2 styles; consider removing good, successful, negative styles
  • [ ] the thing with these numbered styles, is they need a corresponding --code-BLAH= style, and underlines can't be used as the numbered styles include trailing spaces, e.g. --error2='this path is missing: ' --code-error2='a missing path'
• [ ] consider redoing confirm (from #254) with styles.bash rather than echo-style calls