Adding the first pass at a Google Analytics plugin

This includes the backbone.analytics.js file as well as JS and Python style
tests. The server component of the plugin is only for validation of the plugin
setting.
Small comment fix about ga global.
Fixing group member widget routing.
Adding an event for hierarchy widget routing.
Adding analytics for hierarchy widget routing.
Updating jshint version.
Adding plugin documentation.
Merge pull request #312 from girder/google-analytics

Google analytics
Replace mutable default parameters
Simplify chained comparison
Fix spelling mistakes
Fix PEP 8 coding style violations
Remove redundant parentheses
Fix single-quoted docstring
Small CSS fixes
Tweak .gitignore to ignore more coverage files
Add metadata extractor plugin