Update Z shell prompt based on platform

Signed-off-by: Kare Nuorteva <kare.nuorteva@me.com>
Add alias for detecting OS X platform

Signed-off-by: Kare Nuorteva <kare.nuorteva@me.com>
Remove fpath - it is set by default

Signed-off-by: Kare Nuorteva <kare.nuorteva@me.com>
Add system upgrade script

Signed-off-by: Kare Nuorteva <kare.nuorteva@me.com>