replace copied Histogram-code with reference to non-static call

[locked-fg]

A threading issue was caused by static code in JFeatureLib Coloprocessor.
Starting with ImageJ 1.48a there is a non static setRGBWeights method.

Using this method, the copied code can be removed again.

http://imagej.1557.x6.nabble.com/Race-condition-in-ColorProcessor-td5003974.html