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.*

Tools/objj2objcskeleton/objj2objcskeleton

@@ -604,5 +604,6 @@ var NSClasses = {
         "NSWindow" : YES,
         "NSWindowController" : YES,
         "NSWorkspace" : YES,
-        "NSPopover": YES
+        "NSPopover": YES,
+        "NSAppearance" : YES
     };