Adds mentions to reader comment replies

Turns out this covers both if you transition first into a particular post to reply AND for replies directly from the reader.
It's not necessary - good catch.  This two step approach was left over from a more complicated constants based approach.  I've collapsed it into a single visual format language call in https://github.com/wordpress-mobile/WordPress-iOS/commit/570b6f6ccf4137b985438fb8b459b7b172ec62be