BUG: Fixed histogram for floating point volumes

The default behavior of ctkVTKHistogram is that it calculates the histogram to as many bins as many integers are in the scalar range. This results in flat or very choppy histograms for floating point volumes with low voxel values, and results in huge histograms in case of high intensity range. By setting the number of bins to a constant 1000, a reasonable (not too high, not too low) resolution histogram is created for every type of volume.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25939 3bd1e089-480b-0410-8dfb-8563597acbee