Adding non-threaded view to discussion

New non-threaded view for users.

This is the last bit of discussion work for a bit as I am going to go into tidy-up-before-team explosion mode so it will be in a better state to be supported by he whole team and have some tests around it too. There is also loads of duplication etc which needs to be removed.

## See what?
![non-threaded](https://cloud.githubusercontent.com/assets/31692/3286682/b11e2368-f54c-11e3-9f44-c8ab5134a93b.png)
![non-threaded-](https://cloud.githubusercontent.com/assets/31692/3286683/b11faac6-f54c-11e3-9275-b8a2af197079.png)

![Troll](http://i739.photobucket.com/albums/xx36/alux23/troll.gif)
Is `u-h` the right class for that? Shouldn't it be simply hidden rather than accessible to screen readers?