Remove `File Search`

Prior to this commit, Dashboard included `File Search` which was of ...
limited ... value. It required both the file name and the MD5 hash to
search for it in the latest report.  User Experiences was awkward at
best. This commit removes that functionality.
Merge pull request #215 from jeffweiss/remove_file_search

Remove `File Search`
Update db/schema.rb with the new node indexes.
Pluralize the sidebar titles for Groups and Classes.