DOCS-124 Moved all but 2+development version of tutorials and user guides to top-level folders so they
are static and not clogging up Jekyll. Other actual text changes include:
-  Reorganized the user guide and tutorial home pages to emphasize the most recent release
-  Brought _posts/tutorials/music-recommendation/2012-01-01-followups.md into the latest devel branch; this file seems
to have been lost back in 1.0.0-rc4. Content looks like its still appropriate.