Feature: Extended user stats in user export csv

PR to implement this feature:

https://meta.discourse.org/t/extended-user-stats-export-list-plugin/21675/5?u=daniel_fernandez_pes

Comments are welcome!!

Hmm, I'm not sure I like this "syntax", there's way too much `push` for me. I think you could use 2 loops and it'd be better to the eyes ;)