Moved up the installation of oh-my-zsh
- oh-my-zsh automatically changes the shell after installation.
All Casks should be installed to /applications
in the future by default.
Removed macdown.
Use my dotfiles repo to coordinate dotfiles.

Source dotfiles onload
Update Brewfile with latest changes.

May end up using the one in dotfiles repo.
https://github.com/shsu/dotfiles/blob/shsu-10.10/brew.sh