Cut v0.4 release

🚨 Breaking release 🚨 The oceans subpackage, which forms Harmony's Scientific Workbench, has been completely restructured. This means that the API has changed as modules have been moved to new locations. I have tried to update all the notebooks, but I might have missed some.

I have also added an integration test that runs the forward chain of the SWB, and compares the L1 outputs with precomputed expected results. This can help us catch unexpected changes in the behaviour of the forward part of the SWB.