SVGHMI: Naive implementation of widget path substitution in widget DnD: considers widget always have only one variable, and no type checking.

SVGHMI: Widget transform before DnD now have HMI path as a parameter

SVGHMI: Widget transform before DnD now should have HMI path as a parameter, but this path isn't computed for some reason... WIP.

SVGHMI: Widget DnD to Inkscape : Added source SVG widget label parsing and pass selecte HMI subtree to XSLT tranform, so that SVG containing multiple widgets can later be matched against hmi tree fragments, in order to DnD complex groups of widgets.