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.
Incoming suggestion: i've noticed we've got this snippet (shouldAddSuggestionView, based on a blogID) duplicated in few spots. Would it be possible to encapsulate it all in one spot?