Expanded the predefined values in the WidgetState Enum for convenience.  Also added methods to get and force widget states.
Added the resolution header to the graphics header.
Added missing cleanup logic to the UIManager destructor.  Also created destruction methods to the UIManager and AtlasHandler classes.
Changed explicitly set value of Selected state on CheckBox to a reserved state value.
Created the basic skeleton of a MultiImageLayer.  Also created a SingleImageLayer that has all the functionality of the previous ImageLayer class.
Updated EngineDemo "ImageLayer" -> "SingleImageLayer".
Updated Catch "ImageLayer" -> "SingleImageLayer".