Add geological scale

[luanfg]

A core ontology should be able to provide some kind of Geological Scale for its users in order to be able to define the "size" of the objects that users are working on.
A first idea of scale could be the one defined by Della Fávera that is already used to define objects. not sure yet if the best solution is to add scale as a BFO quality or some other concept.

[luanfg]

Reference for Della Fávera's scale:
Fundamentos de Estratigrafia Moderna, J.C. Della Fávera, 2001.