Fixes to appkit bindings

Implement NSFrameRectWithWidthUsingOperation, missing from [NSGraphics.cs](https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Miscellaneous/AppKit_Functions/Reference/reference.html#//apple_ref/doc/uid/20000695-SW35)

Added [NullAllowed] attribute to NSOutlineView expandItem:expandChildren: (as per the [documentation] (https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSOutlineView_Class/Reference/Reference.html), "Starting in OS X version 10.5, passing 'nil' will expand each item under the root in the outline view."