Handle multiple species

[hansvancalster]

The current code was created with a single species in mind. Handling multiple species would be something to add in a future PR. Handling multiple species in the same database would require a different database structure. We could to add a global function that combines connect_db(), import_observation(), distance_matrix(), cluster_observation() and get_cluster(). That should make it easier to handle multiple species while using a separate database for every species.

Originally posted by @ThierryO in #2 (comment)

[ThierryO]

The question is how to handle multiple species? By looping over the species and handling them one by one?