Some vessel performance models (e.g. SDA) contain hard-coded calculations e.g. on ice_resistance and fuel_eq. It would be nice to abstract more of this out to vehicle configs.

We can then trim some of the vessel performance models defined as vessels, and replace them with more example configs.

Part of the reason for doing this is revisions we want to make to in-sea ice navigation behaviour of the SDA. Testing and benchmarking through various configs will be easier and more systematic than changing the model itself between versions.

Also see #327