updated threshold plugin to work with 'above' operator

I have updated the threshhold plugin to work with the 'above' operator. It is now possible to color a data point if it is below a value OR above a value. This is useful for any data that may have an ideal range (E.G.: between 4 and 15); you may wish to color any bar below 4 or above 15 as red to indicate outside of preferred range.