Adding a comment when in the middle of a discussion

# What?
* We needed to be able to add a comment when someone was in the middle of a conversation.
* What we are doing is adding the new comment to a new-comments container.
* We can then scan through this and make sure we aren't loading their comment into the stream. If we are, we remove it from the new-comments container.

# Why (all the refactoring)?
We had a slightly different UX decision at the beginning as to how this would work, leading the [`comments.js`](https://github.com/guardian/frontend/blob/master/common/app/assets/javascripts/modules/discussion/comments.js) to be heavily refactored. 

The decision was then changed leading to a simpler UI and, potentially, a smaller code change, but as the refactoring had been done, I thought it would be nice to keep it.

This will also help us when we get onto sorting etc.

The branch name is a little misleading due to this too.

![yapyapyapyap...](http://stream1.gifsoup.com/view1/1171127/talk-too-much-blah-blah-blah-o.gif)