EclipseWriter: support reordering of compressed cells.

This commit removes the implicit assumption that the cells are ordered following the Eclipse Cartesian logic 
( e.g. as made sure by this two assertions:
assert(compressedToCartesianCellIdx[i] >= i);
assert(i == 0 || compressedToCartesianCellIdx[i - 1] < compressedToCartesianCellIdx[i]);
)
Now arbitrary cell orders are possible and data is remapped to the Eclipse order upon write. 
Of course, both implementations do basically the same. But once the compressedToCartesianCellIdx is used and once the gridToEclipseIdx. Both exist and both are different. On top of that one is copying from a large azrray (all cells) to a smaller array (only active cells) while the other one is reordering the vector contents. I can put this into one method. I don't think it matters all that much.