Added xPartition.h where can be found the definition of xPartition and
    xGetPartition

    Added xIter.h where can be found the definition of xIter and xClassIter

    xScalarFunctionDerivDiscXFEMOctree, previoulsy in xApproxFunction.h is
    moved to it's own file : xApproxFunctionDerivDiscXFEMOctree.h

    datamanagerxMesh_t and partmanagerxMesh_t are removed.

    Other files are modifyied accordingly and clang-formated.