LIE; Update Heaviside function to [-1/2,1/2] range.

Due to incorrect results for a Neumann type BC (traction) on boundaries crossed by a fracture the Heaviside function for levelsets was changed from [0;1] range to [-1/2;1/2] range. The corresponding postLIE tool was updated too.

The test is a five element test (three quads stacked with two fractures); The bottom and left boundaries are held fast the top and right boundaries being pushed/pulled. The test produces obviously incorrect results in the master-branch version.

Because of the change of the Heaviside function all of the references were updated. To ensure validity two comparisons were performed:

1. All of the ctests passed but those for displacement/displacement_jump/stress variables.
2. All of the ctest results were processed with postLIE tool and the resulting u displacement was compared to the master-branch version (processed in the same way) matching up to 1e-16 in absolute or relative errors.

find -name '*.vtu' | while read i; do ~/w/ogs/r/bin/postLIE -i ${i} -o ${i}_post.vtu; done 
find -name '*_post.vtu' | while read i; do ~/w/ogs/r/bin/vtkdiff -a u -b u ../master/${i} ${i} --abs 1e-16 --rel 1e-16 >& ${i}.vtkdiff || echo $i; done

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The merge request is two-fold:

• The first part is generalization of the code w/o any changes to the benchmarks.
• After changing the Heaviside function a new test is added and references update.

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1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?