Add more information to the list of classes on a package

[moufmouf]

On a package page (e.g. http://packanalyst.com/package?name=symfony%2Fhttp-foundation&version=dev-master), we could add some information on each class/interface as to how many time they are used / extended.

Idea initially proposed on Reddit: http://www.reddit.com/r/PHP/comments/2r38m5/packanalyst_explore_php_classes_from_packagist/