Add @mention suggestions to the "long form" iPad commenting flows

That is, the flows that include the "tall" (multi-line) EditReplyViewController, which is used on iPad for both notifications and me>sites>comments.  This fixes #2699 

Also avoided adding SuggestableView to IOS7CorrectedTextView per discussion with @jleandroperez 

Also tested to ensure this does not cause regression on ReplyTextView.
Agreed.  Fixed in https://github.com/wordpress-mobile/WordPress-iOS/commit/a2c852e2c97a2c79bee14f4ac65671a012b1dc62