Implement ray aberration curves

[GNiendorf]

These curves would be very valuable for the optimizer, which currently only optimizes for the rms of a spot diagram

[GNiendorf]

http://www.faculty.virginia.edu/ASTR5110/lectures/optics2/optics2.html

Good article on an implementation (only read the first part which seems most relevant)

Another good article: https://eckop.com/measuring-aberrations/

[GNiendorf]

Partially covered by PR #9. Still need sagittal plots.