Adds the verification of the OWSMapContext on the valadation of the GraphicalElement.
Update the ConfigurationAttributes and add the values limits to the Numeric attribute.
Now it's the UIController that knows which GraphicalElement is selected (and not the ConfigurationShutter),
The ConfigurationShutter display a list of ConfigurationAttributes an not an element.
Enables the GraphicalMultiselection but the abstact key word is removed from GraphicalElement,
Adds a cloning constructor,
Adds a function giving back the nearest common superclass in GraphicalElements.