fandoms | users | works numbers on homepage are hard to parse

Currently, the homepage displays the (somewhat rounded) number of fandoms, users, and works to logged out users. These numbers don't have thousands separators, however, which makes the user and work figures almost impossible to read at a glance:

more than 31950 fandoms | 1881000 users | 4733000 works

We'd like to add some separators, and since the site is currently in American English, this should be commas. Once we have the site ready for i18n, this is easy to configure for other languages.