ENH: Add mirror pad option to ImageMath
ENH: Add mirror pad option to ImageMath

- specify the number of voxels to pad for all image faces.

LucasGandel/TubeTK,KitwareMedical/ITKTubeTK,thewtex/TubeTK,KitwareMedical/TubeTK,sumedhasingla/TubeTK,KitwareMedical/TubeTK,matthieuheitz/TubeTK,LucasGandel/TubeTK,LucasGandel/TubeTK,cdeepakroy/TubeTK,aylward/ITKTubeTK,sumedhasingla/TubeTK,matthieuheitz/TubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/TubeTK,KitwareMedical/ITKTubeTK,aylward/ITKTubeTK,LucasGandel/TubeTK,matthieuheitz/TubeTK,sumedhasingla/TubeTK,matthieuheitz/TubeTK,thewtex/TubeTK,cdeepakroy/TubeTK,KitwareMedical/ITKTubeTK,cdeepakroy/TubeTK,aylward/ITKTubeTK,KitwareMedical/TubeTK,thewtex/TubeTK,aylward/ITKTubeTK,sumedhasingla/TubeTK,thewtex/TubeTK,cdeepakroy/TubeTK