[FBref] Add unique identifiers to players and teams datasets

[lorenzodb1]

FBref provides a unique 8-character ID for each player and team. This can be particularly useful when working with large datasets. I was wondering if we could include this in the data returned by the scraper.

The following is an example of the IDs provided: fbref.com/en/players/c115db1e/Dailon-Livramento

[probberechts]

Yes, good idea! Would you be able to implement this?

[MartiONE]

I can do this @probberechts if @lorenzodb1 is OK with it :)