Grid generation

[jasontempestholt]

Easiest to generate grid when i,j axes align with polar coordinates, so:

1. Rotate to coast/shelf break
2. Enlarge to cover all of original region
3. rotate to equator
4. Rotate back to align with polar coords
5. Generate equal angle grid
6. Rotate to coast/shelf break
7. Rotate back to original position
8. Interpolate classification to grid
9. Truncate grid to exclude all-open ocean and all-land rows/columns