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.

SVGHMI: Widget Library Picker now transforms SVG widget before allowing DnD. Transform is just identity forn now, but label parsing have already been included. To be continued.

SVGHMI: Ensure that when widgets are nested in HMI:Switch widget, their sub-elements are taken as switch's choice in case their label match the syntax.

SVGHMI: Code cleanup for ToggleButton.