Add commit history on folders (BB-8483)

Hi,

one of the top features I love GitHub for (I hope you don't mind comparing you guys to GitHub) is the ability to view the commit history for a folder.

For example: https://github.com/symfony/symfony/commits/master/src/Symfony/Component/EventDispatcher

The link above displays the commit history for src/Symfony/Component/EventDispatcher folder of the repository in a way that all commits that didn't touch the folder and any items inside of it are just filtered out.

In other words, only commits that changed something inside that foder are displayed.

Since viewing commit history for a folder in git is simple as git log src/Symfony/Component/EventDispatcher, I suppose this should be trivial to implement.

Thanks for listening!