Threshold fixes

A few fixes were made to get thresholding using Otsu to run and produce the right result.  A simple global threshold test was added to test the changes.   I also tested the changes by running Otsu threshold within a more complex jython script and it looks to be producing the correct result.

1.  In HistogramCreate.java the 'countData' function is now called to generate the histogram. 
2.  In Global Threshold the map needs to be passed the thresholdOp (instead of the threshold).  
3.  In Otsu the bin number needs to be translated to a gray level threshold (please let me know if the Otsu function was intended to return a bin number, if so I can calculate the gray level somewhere else). 
4.  A GlobalThresholdTest was added.