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.

          <xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>