SVGHMI: fading page switch : defer update of classList to next animate() call when finishing transition.

classList update was happening in the same call as switch_page(), but this call is not meant to do any change in the DOM. This was triggering unwanted style and layout recomputation.

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="WAMP://127.0.0.1:8888#Automation#wamptest">
  <TargetType/>
</BeremizRoot>