SVGHMI: Add inhibition to widget's apply_hmi_value() so that it does not change variable more frquently than given widget's frequency. This prevents flooding network with many update if browser is producing events at high rate, as for exemple when dragging ScrollBar's cursor.

          <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"/>