More work on child windows

- Popovers are implemented as child windows.
- Renamed _CPAttachedWindow/_CPAttachedWindowView to _CPPopoverWindow/_CPPopoverWindowView, since that is its only use.
- The default for CPView -acceptsFirstMouse is now NO, per Cocoa. Subclasses override this as necessary.
- _CPWindowView -hitTest returns self it the mouse is within a resize region, which may be outside the window's frame.
- Fixed an off by one bug in CPDomWindowLayer -insertWindow:atIndex:, where inserting a visible window behind a window it is already behind would cause it to move up one from its intended position.
- Updated the ChildWindows and CPPopover test apps.

AppKit/_CPImageAndTextView.j

@@ -105,6 +105,7 @@ var _CPimageAndTextViewFrameSizeChangedFlag         = 1 << 0,
         }
 
         _textSize = nil;
+        [self setHitTests:NO];
     }
 
     return self;