Add OAE proxy

[coroa]

1. Gridding using a uniform ocean mask (together with EEZ based country masks) leads to uniform depositing within each countries EEZ. Implemented within reorganizing and adding docs #35 (02e955c especially).
2. There are also OAE efficiency maps available now: https://www.researchsquare.com/article/rs-4124909/v1
3. Also waiting for wider discussion