Changes for 2.2.12

• We have been optimizing the space used by GraphObjects. The heap used by typical large diagrams now occupies about 10% less space. Creating copies of a lot of nodes and links may be a bit faster now too.
• Fixed the new PanelLayoutFlow extension so that multiple "Flow" panels can coexist in the same panel.
• Improved GenogramLayout in the Genogram sample to support a horizontal direction as well as the standard vertical direction.
• Improved the Selectable Fields and Selectable Ports samples so that clicking on fields or ports within a node respects the Control and Shift modifiers to toggle or add to the collection of selected fields or ports.
• Fixed object picking (Diagram.findObject, GraphObject.containsPoint, etc) for Shapes with a GraphObject.background.
• The Group.layout property setter now checks to make sure that the new layout is not also the value of Diagram.layout.