Create getGrid_() methods for debugging pursposes for HEXAGONAL grid layout

[vkovtun]

This is a feature suggestion.

Currently the methods getGridX(), getGridY(), getGridZ() of the CubeCoordinate class show the grid cube coordinates with the origin (0, 0, 0) on the top left, which is outside of the grid if the layout is HEXAGONAL. Having the origin in the center of the grid would be more useful.