BUG: Changed segmentation combobox behaviour in slice controller

The segmentation combobox in the slice view controllers showed any hidden segmentation that was selected (thus the eye icon seemed not to be updated). This is now turned off, so changing selection itself does not change segmentation visibility. Also the None item in the combobox is now removed, as it was related to the above function.

Failing segmentation test has also been fixed.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25369 3bd1e089-480b-0410-8dfb-8563597acbee