Avoid link farm - external links should have nofollow attribute

It would be good to mark all external links (other than our own domain and CDN, custom domains list specified by the Admin in the Settings area) as rel=NoFollow link (including text links, embeded images etc) just to avoid building a link farm from our community ("Page Rank power").

If a post/comment will have some affiliate links there should be also a possibility to mark it as Sponsored (although NoFollow should be sufficient).

BTW: links to user-generated content should be marked with rel=UGC.