Range slider widget forces the wrong processor to be enabled

The range slider widget forces that the base slider processor is activated via isPropertyRequired() implementation, but it should be the range_slider clearly. Not only that this does not guarantuee that the really needed processor is enabled, this is actually forcing a misconfiguration resulting in SliderProcessor::postQuery() getting executed twice - one time from the range_slider processor itself and one time per directly calling the parent SliderProcessor class.