We were looking up each mention one by one without any form of caching and that results
in a problem somewhat similar to an N+1. When we have to do alot of DB
lookups, it also increased the time spent in the V8 context which may
eventually lead to a timeout. The change here makes it such that mention lookups only does a single
DB query per post that happens outside of the V8 context.
* Adds primary user group as a class to quote
This feature addition will add the class `group-PRIMARY_USER_GROUP` to
the quote `aside`. `PRIMARY_USER_GROUP` will be the primary user group
of the user being quoted. This is similar to the class that is added to
a `topic-post`.
* Remove trailing whitespace
* Fix avatar in test
* Address PR comments
* Fix trailing whitespace
