Move .oh-my-zsh/custom into a top level directory

I added a custom plugin and some custom themes to .oh-my-zsh/custom, but
.oh-my-zsh is in its own git repo. I want to keep my customizations all
in this dotfiles repo so moved it out to a top level directory and am
symlinking it into .oh-my-zsh.

    ln -s .omz-custom .oh-my-zsh/custom
Add extra spacing after the emoji prompt