Bugfixing all over, but most prominently in a change to GUISubcontext.
GUISubcontext now has a renderSubcontext method that renders the
subcontext within the currently set clipping area of the given graphics
and by the end of the method the graphics has the same clipping area as
it did at the method call.

Added CollapsibleFrame, a collapsible GUISubcontext that only
updates/renders its subcontext when expanded.