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.
(I would just add it to the main project). Reason why is: it's just simpler to have it there (that's just my opinion!).

We already have a couple WPStyleGuide+Something categories: [ReplyTextView](https://github.com/wordpress-mobile/WordPress-iOS/blob/develop/WordPress/Classes/ViewRelated/Notifications/Style/WPStyleGuide%2BReply.swift), [Comments](https://github.com/wordpress-mobile/WordPress-iOS/blob/develop/WordPress/Classes/ViewRelated/Reader/WPStyleGuide%2BComments.swift) aaand [Notifications](https://github.com/wordpress-mobile/WordPress-iOS/blob/develop/WordPress/Classes/ViewRelated/Notifications/Style/WPStyleGuide%2BNotifications.swift).

Thank you Allen!!