submitHelper module

Fixes #1830 

Takes over `uncheckSendRepliesToInbox` functionality from betteReddit.

Currently the repost warning box is styled with reddit's classes (so it could potentially be mistaken for native functionality). Is it enough to make the feature disabled by default, or should it be more obvious that it's a feature of RES and not reddit?
I also had to remove the ability to search the text of self-posts to reduce false negatives, but I don't think that's too big of a deal.
re: pages with different `#sections` - iirc the user wanted us to match the page regardless of section, because reddit will treat it as the same page.

And that makes sense, I think I will keep the entire query string, we might as well stay on the safe side.