ENH: Changed default segment editor threshold max to image max

As susggested by Steve Pieper: I usually find people use the default when they want skin and bones vs air and cutting off the top of the range could lead to a lot of noisy holes in the segmentation (that take a long time to process as surfaces).

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25415 3bd1e089-480b-0410-8dfb-8563597acbee