Align terminology in `data.spec`

[tnatt]

Currently we have deviating terminology in the spec field for different objects.

• ncol vs num_columns
• nrow vs num_rows

We should aim to make the datamodel consistent where we can and align on one of these.

The nxxx syntax is short and in line with Xtgeo, but the other is more explicit.

• If we go for the nxxx syntax should we change num_vertices to nvertices and num_triangles to ntriangles for TriangularSurfaces ?
• If we go for the more explicit should we also look into other changes e.g. xori to x_origin ?