[Opm] Reorganization of modules: opm-polymer and opm-autodiff

[Atgeirr Rasmussen]

> 3. des. 2015 kl. 13.33 skrev Atgeirr Rasmussen <Atgeirr.Rasmussen at sintef.no>:
> 
> If no-one objects I intend to do the reorganization early next week.

This has now been done, and all contents of opm-polymer is now in opm-autodiff.

Special thanks to Arne Morten Kvarving who managed to combine the repositories
without losing any commit history!

Atgeirr