Removing redundancy in Triangulation

[DanielVandH]

There is a bit of redundancy in the fields of Triangulation. I would like to remove the triangles field for example and possibly let Graph be lazily computed (or initially empty and then populated when calls to it are made.. I don't remember where it is strictly needed in the algorithms themselves, or if I've just used it for convenience).

This isn't technically breaking but I've seen a lot of calls to the .triangles field that it would be best to wait for 2.0 anyway.

[DanielVandH]

Adjacent2Vertex could also be implemented in a smarter way. It would just be hard to use for the user after the fact.