Rename fine distributions to BMMs

[pawel-czyz]

This PR is, as proposed by @grfrederic, about updating naming conventions.

Tasks:

• [ ] Change the import in the package. (from ... import ... as bmm rather than from ... import ... as fine)
• [ ] Update unit tests.
• [ ] Update Snakemake workflows.
• [ ] Update the documentation: check if API is rendered properly.
• [ ] Update the documentation: adjust the tutorial.