Support sphingolipids naming convention

[comcon1]

New naming convention developed with @tfmFerreira is now represented in the main repo.

• tail retrurning function counts 'fa' and 'sphingosine' as tails
• NMRPCA consider two-tailed sphingolipids egligible for the analysis
• Documentation reflects the convention
• Molecule list in the documentation is dynamically updated from the testing web portal
• Pretty numerator supports new sphingolipids to number them properly

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📚 Documentation preview 📚: https://databank--475.org.readthedocs.build/

[comcon1]

@ohsOllila @markussmiettinen I want to draw your attention to the fact that the naming convention of sphingolipids has been changed during our meeting with @tfmFerreira. After this PR is approved and merged, if we find some of the lipids that don't align with this convention, the mapping files must be adopted, and not the code.

[mdondrup]

Hi, I think you should be able to approve this quickly. I have run an import check, and this branch is shown as the current state on the test server.

[mdondrup]

I just saw that I could review, so I approved. The changes seem sound. Ofc I don't know exactly what you @tfmFerreira and @comcon1 discussed.