Fix the issues #8, #9, #10, #11, #13.

Fix the issues #8, #9, #10, #11, #13 @gpetit ,

Issue #8 : For the GraphicalElements using a SourceCA, keep in memory the last used path and use it as default for new GE.
Issue #9 : All the spinner for numeric value can be changed by using the mouse wheel.
Issue #10 : Double clicking on a GraphicalElement open the ConfigurationDialog for this element while clicking on the toolbar button 'configuration' open the ConfigurationDialog for all the selected GE.
Issue #11 : When the user creates an Image GE, the ratio between width and height of the image can be kept on drawing the GE bounding box.
Issue #13 : Creation of an overlay to the CompositionArea to permit to the user to draw with the mouse the size of the new GraphicelElement. If the GE is an instance of Image, by olding the shift key the drawing keeps the image ratio between width and height.

Now when the user creates an new GraphicalElement, he can do the GE configuration and the drawing of the GE bounding box at the same time.