Circular dependencies, but git is not needed

git will always be installed on OS X, which is the only platform
usable with homebrew.
Use the :app template for Dropbox, not :cask

As we need the ssh keys, which is stored in Dropbox, for cloning the
brew cask repos, Dropbox cannot be installed through brew cask.
Add mps-youtube

This is a terminal based YouTube player and downloader.