Add analytical elliptical test case

[jellepoland]

Described in p.10 and 11 of Simonet et al. (2024)
URL: https://doi.org/10.21203/rs.3.rs-3955527/v1

• Do check if this is the same, or not the same, as the 'elliptical_wing' test case

There is a difference between the reference Chattot results:

And the reported reference case by Simonet

The difference is most clear when checking the maximum CL, which occurs close to 50 for Chattot and close to 60 for Simonet.

The difference is due to a difference in AR, Chattot = 12.7, and Simonet = 5.

The VSM does not find the same solutions, is not as close.
BUT, the resulting circulation distributions are much much smoother, which is good news.

TODO

• Make new test case into a test
• Change naming of OLD test
• Change old test, it should only compare LLT and VSM with the analytical equation for high AR. The test is mainly usefull for high AR.