REALMET: Improve the hashcode implementation of the neighbourhoodLattice2GraphShape transfomration

[ArenBabikian]

Currently, for the neighbourhoodLattice2GraphShape transformation, the hashcode calculation is buggy. It throws a stack overflow error whenever it needs to be calculated (ex. for GraphNodeDescriptorGND objects, when we want to store it in a List), possibly because of an infinitely recursive call to the hashcode calculation function through the IncomingRelationGND and OutgoingRelationGND classes. This should be fixed in a manner similar to that used by Oszkar for the neighborhood lattice creation, in the [Descriptor ](https://github.com/viatra/VIATRA-Generator/blob/RealisticMetrics/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.partialinterpretationlanguage/src/hu/bme/mit/inf/dslreasoner/viatrasolver/partialinterpretationlanguage/neighbourhood/Descriptor.xtend)file.