FIX: Fix ImageMath CLP loading in slicer/prometheus

Loading ImageMath in Slicer as an exec was causing it to crash (Debug mode,
in Release the module is ignored). The use of the character '<' created
mismatching tag in the xml.

Change-Id: Ic3424eadf36594708008cc92938455d84d121b9f
Merge pull request #262 from vovythevov/fix-image-math-CLP

FIX: Fix ImageMath CLP loading in slicer/prometheus