refactored context api - top() is now a simple get on context::$context
refactored context api - top() is now a simple get on context::$context

mjrider/arc-events,mjrider/arc-config,mjrider/arc-web,mjrider/arc-xml,Ariadne-CMS/arc,mjrider/arc-grants,mjrider/arc-cache,mjrider/arc-base