ENH: Clean up ThresholdAnImageUsingOtsu

Removed uneccessary update calls in the c++ code, and cleaned up the code to be consistent with the binarythresholdfilter
Added the python example

Change-Id: I8e6bca62a90e66c3fac423479afc9c20d015cc66
Merge "ENH: Clean up ThresholdAnImageUsingOtsu"