Pluralize Groups and Classes in the left sidebar, update db/schema.rb

Add the indexes to db/schema.rb from the migrations after merge of #188 

Update the sidebar titles to be plural.

![Screen Shot 2013-04-19 at 6 51 54 AM](https://f.cloud.github.com/assets/39406/402202/6fd598c4-a8f8-11e2-9a2d-c79a902cb392.png)