Update DgmOctree syntax (#100)

* Improve the syntax of ScalarFieldTools::computeCellGaussianFilter

* Syntax fix

* Restore the definition of DgmOctree::MultiThreadingWrapper in the header to avoid issues when linking CCCoreLib statically on Windows

New 'robust' option for the C2M algorithm to compute determine the si…

…gn of the Cloud/Mesh distances in a more robust way (but with added computation time)

Bug fix (#87)

* Bug fix: it seems the search ROI can fall outside of the grid when looking for the nearest triangles inside a grid/mesh intersection structure

* Update the syntax to avoid exposing the Octree multi-threading structures and the ENABLE_MT_OCTREE preprocessor

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Co-authored-by: Daniel Girardeau-Montaut <DGirarde@its.jnj.com>