Draft: Resolve "Ckdtree without cartesian coordinates in grid file"

If cartesian coordinates (cell_circumcenter_cartesian_x/y/z and cartesian_x/y/z_vertices and edge_middle_cartesian_x/y/z) are not present within a grid file, we derive those coordinates from clon, clat, elon, elat, vlon and vlat, respectively.

Closes #10 (closed)