Add different models

[luanfg]

We are dealing with models in Geology that are 3D or 2D.
3D Models could be:
3D Diagram Block - It is a drawing based on a conceptual model.
3D Grid - A grid that is based in some structural scheme which is grided. This is typically the model that is created for upscaling later on and use as a base for a flow model.
3D Geological Model - This is neither a 3D DB nor a Grid. It is a conceptual model that is is not necessarily a block.

2D models are usually cross sections.

[luanfg]

We still need definitions for 3d grid and 3d geological model.