SVGHMI: attempt to optimize for webkit, because of really slow style recompute in svg:use : "unlink clones" (as in inkscape) but stop deep-copy when meeting a widget, and create a new clone instead.

SVGHMI: optimize browser work by hiding (display:none) pages that are not displayed.

SVGHMI: Better and less verbose SVG namespace handling in XSLT transform

SVGHMI: Added mostly untested switch widget