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.
Sure!  You mean to move this to the WordPress-iOS-shared pod, https://github.com/wordpress-mobile/WordPress-iOS-Shared/tree/develop/WordPress-iOS-Shared/Core , right?  e.g. Core/WPStyleGuide+Suggestions ?  Or do you mean to move it to be a category in the main project in Classes/Categories?