Update Durham tutorial

[andreufont]

I just checked that it doesn't run (we have moved poly_p1d to utils).

It would be good to have all notebooks running before the workshop.

[lauracabayol]

I have fixed this in the latest extended emulator branch commit

[jchavesmontero]

It is also running in the nyx_cosmo branch. We can close this issue after any of you (@andreufont , @lauracabayol ) verify this

[andreufont]

I can run the notebook, but I would probably add a warning in the notebook itself that the code related to the Nyx emulator will not run if you do not have the (private) Nyx files. You could also add a link to the NERSC location where these files are.