Finish out NerdTabViewController by adding individual images to the tab buttons for each view controller. The user will almost certainly enjoy being able to differentiate between the tabs.
To do this you need a way to tell the tab view controller what image to use for each tab. One approach would be to write methods for adding the child view controllers which take an image for the tab:
func addChildViewController(childViewController: NSViewController, tabImage: NSImage)
This would work, but it is not a great choice because it calls into question the ...