Adds mentions to reader comment replies (both if you transition first into a particular post to reply OR for replies directly from the reader).
Merge commit '9bba5a9a58aeaef5968255e766d9489a65294326' into issue/2699-add-mentions-to-reader-detail-replies

Conflicts:
	WordPress/Classes/ViewRelated/Reader/ReaderCommentsViewController.m
Simplify constraint code into a single VFL call props @aerych
Instead of adding and removing the off-keyboard gesture recognizer, let's just enable and disable it as needed.  Props @aerych
Move the adding of the tapOffKeyboardGesture recognizer to viewDidLoad, initially disabled, and instead have the textShouldBeginEditing delegate enable it.  This avoids potentially adding the recognizer twice. props @aerych
Merge remote-tracking branch 'origin/develop' into issue/2699-add-mentions-to-reader-detail-replies
Merge pull request #2707 from wordpress-mobile/issue/2699-add-mentions-to-reader-detail-replies

Adds mentions to reader comment replies - props @aerych for the thorough review