Replying to a topic visually updates watch star on topic

Rebuild topic title bars on post actions.

In order to do this, we have to output the entire topic in the API
output.

Fixes issue where watch status is not updated on client-side after
editing or replying to a post.

Change-Id: I63563c44ed10c0cdcb399f18c6f900df78012d17
Merge "Replying to a topic visually updates watch star on topic"