COMP: Added new unit tests for increasing code coverage

Added new testing code for TriangleMeshToBinaryImageFilter,
ErodeObjectMorphologyImageFilter,
SignedMaurerDistanceMapImageFilter,
SignedDanielssonDistanceMapImageFilter,
DoublThresholdImageFilter,
MorphologicalGradientImageFilter

Change-Id: I15eed6a350d1d49cfdbbdd0587a85821a766ecdd
WIP: Testing zero buffer optimization.

Change-Id: I0ef74e9942ee278b056d7e0ef8de4053876d7211
WIP: Use minimum buffers.

TODO:  Need to review failng testcase.

Derivative values seem to be wrong.

Change-Id: I216c1108853d87378de2773b653d8ccd1e1fd505