NEW: Initial support for CPAppearance

This patch adds the `CPAppearance` class and uses it where needed.
There is nearly no impact, but in `_CPPopoverWindowView` where the
`CPPopoverAppearance` needs to be converted to a `CPAppearance` object

nib2cib support has also been added.

*This patch brings no new functionality.*

AppKit/AppKit.j

@@ -26,6 +26,7 @@
 @import "CPAccordionView.j"
 @import "CPAlert.j"
 @import "CPAnimation.j"
+@import "CPAppearance.j"
 @import "CPApplication.j"
 @import "CPArrayController.j"
 @import "CPBezierPath.j"
@@ -109,4 +110,4 @@
 @import "CPWebView.j"
 @import "CPWindow.j"
 @import "CPWindowController.j"
-@import "CPWorkspace.j"
+@import "CPWorkspace.j"