Add BacDive-IDs to large, returned list

[katrinleinweber]

Instead of leaving the index numbers [[1]], [[2]], etc. the datasets should be named according to their bacdive_id. Which is not in the dataset itself, so it might need to be spliced out of the URL again, or retrieved from a previous, ID-containing vector.

Probably needs to be assigned in https://github.com/tibhannover/BacDiveR/blob/master/R/retrieve_data.R#L66-L70