Add experimental graphql endpoint

[GianlucaFicarelli]

Add an experimental graphql endpoint, reusing the existing service logic.

• Accessible at http://127.0.0.1:8000/graphql
• Only species and morphologies can be retrieved and modified.
• Graphql would have its own error handling according to the specs, but it is temporarily bypassed

This is a showcase, not to be merged.

[g-bar]

Really cool, thanks for the showcase.