[Opm] Important module structure change: opm-material folding into opm-common

[Atgeirr Rasmussen]

Dear OPM community,

Tomorrow, Friday December 9 2022, at 12 CET, we will merge the following PR:
https://github.com/OPM/opm-common/pull/3234
as well as companion PRs in opm-models and opm-simulators.

>From that point, the opm-material repository will be deprecated, and all its code will be moved to opm-common,
including its commit history. Header files will be available using the same #include paths as before, they will just reside in a different module. If you have modifications or branches in opm-material that you would like to keep alive, they should be transferred to opm-common. We may provide guidance if necessary.

This means that you may have to change any build scripts or setups you use. The change should probably be quite simple though: you no longer need to include opm-material in the set of modules to build.

Big thanks to Arne Morten Kvarving for doing this simplification!

Best,
Atgeirr Flø Rasmussen