Folding UWGeodynamics into Underworld

Yeah, one repo, one vision!

In an effort to simplify maintenance and compatibility between Underworld and UWGeodynamics, we have decided to merge the codes into a single  repository.

Starting with version 2.13, UWGeodynamics will now live under Underworld.

All UWGeodynamics functionalities and workflows will remain available to the users. From version 2.13 users will be able to import UWGeodynamics after installing Underworld (see documentation for install options), using from underworld import UWGeodynamics.

Issues, functionality requests and pull requests will have to be submitted to the Underworld repository.

The UWGeodynamics repository has been archived and is now read-only. Older versions of UWGeodynamics will remain available but will NOT be made compatible with newer versions of its dependencies.

We encourage users to update their Underworld package as soon as possible.

We understand this can be an inconvenience to some users. This will allow us to focus on development by reducing maintenance work.