Remove shit from our .gitignore list

At the very beginning, we commited tons of shit we want to ignore.

Delete everything that matches our .gitignore file, so that we no longer
track it. To do so you run:

git ls-files -ci --exclude-standard -z | xargs -0 git rm --cached

See this discussion for more:
http://stackoverflow.com/questions/7527982/applying-gitignore-to-committed-files