New script: Color Picker

A simple script to bring up the OS X color picker dialog.

Note you can use `choose color default color {0, 65535, 0}` to make it come up with a different color.

I found this on this repo: https://github.com/prokizzle/LaunchBar-Scripts/blob/master/Color%20Picker.applescript

Couldn't figure out how to pull in certain commits only, so I just whipped up my own.