Preventing N tag queries on post index pages

[spilliton]

Every post partial calls .tags which causes a query per post. Adding :tags to the includes should bring this down to a single query instead of N queries.

[jipiboily]

Thanks! Looks legit.

Monologue requires attention (paying $100 to get it upgraded to Rails 5, see #314 hold before merging as the test suite is failing for this PR (and all builds, btw).