introduce newer version of docbook-xsl themes
direct stylesheets to use newer DocBook XSL version
new images - for GitHub guidance
change Assembla references to GitHub
ignore compiled help
Update README.md
Update **keeping in touch** guidance.
Merge pull request #614 from debrief/feature/ian/keeping_in_touch

Update **keeping in touch** guidance.
drop embrionic (DITA-based) guidance
minor refactoring to intialiser setup. Only show solution is it's not a monster error.
minor changes, restructuring
code auto-clean up
Merge pull request #615 from debrief/598_duff_solutions

598 duff solutions
Include "in-progress" issues
Update README.md
refactoring, to let us keep the old set of track segments after a merge
forget about legacy folders inside help folder.
Use our new Merge Tracks processing, instead of the old one using the TrackWrappers organic merge method
Merge pull request #616 from debrief/589_keep_merged

When merging tracks, we should not delete the old one, just hide it. closes #589
* tighter Class checking on merge operation
* hide TMA solution after converting to legs/standalone track