Make Cli a real class
Implement `date_of_last_commit` in SourceControlSystems
Calculate the date of the last commit of each file

I don't like putting this inside the Churn class, but I don't see where
else it should go.
Start file ratings
Show file ratings in the code index page
Show file rating in the file code page
Prettify code ratings
Improve (?) ratings calculation
Show the date of the last commit of each AnalysedFile
Change view helper javascript_path to javascript_tag
Use timeago.js to live update dates
Encapsulate analysed_files initialization in a module
Make SmellsStatusSetter a module instead of a class
Make Turbulence a module instead of a class
Move `smells_at_location` logic to its rightful place: AnalysedFile
Rename Serializer class variables
Fix test which was not passing on Windows

(Not that it matters much, really...)