This change also changes context detail page URLs from /context/my_context to /contexts/my_context
Add a database index on the projects and contexts tables, user_d + name, to speed the lookup used in urls
Brought the URLs within various feeds up-to-date
git-svn-id: http://www.rousette.org.uk/svn/tracks-repos/trunk@399 a4c988fc-2ded-0310-b66e-134b36920a42