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"?>
<BaseParams Name="py_ext_0" IEC_Channel="0"/>