Renames the challenge problem to use group as a variable name instead of class.
Make scaffold/migrate/server separate steps.

Many students at the intermediate railsbridge were accidentally pasting the three lines as one and ending up with a very strange migration. I've made these separate so that it is more clear that it is 3 distinct steps.
Merge branch 'patch-1' of https://github.com/jessetoth/docs into jessetoth-patch-1
Updated for Windows 8 based on Feb. 8 InstallFest in San Francisco

  - Instructions to install Node.js for Windows 8 only to address
    coffeescript compilation error (even on empty files)
Advise Windows 8 users to reboot after installing Node
Fix sidebar links on /docs site