dry-up and cleanup in zshenv and zshrc

did a cleanup based on comments in thoughtbots
laptop skript and dotfiles:
* moved all PATH settings to zshenv and removed /etc/zshrc
* added a few zsh options
updates atom config
updates list of brew cask apps

* adds virtualbox
* adds vagrant
adds aliases

* adds alias file for server aliases in seperate private dotfiles directory
* adds alias to update rbenv
* adds alias to edit dotfiles