Add in a short delay when opening the terminal on OSX

Allows for users with `~/.bash_profile` setups that open tmux, screen etc.. by default to launch the Julia app properly.

See https://github.com/JuliaLang/julia/pull/3547 for discussion. A better implementation would be a command to Terminal.app to not start a shell that reads these customized scripts, however a search for such a command has been unsuccessful.