Use new + icon as a show more button on fronts

Discussion can also use these icons for "show more comments", they are simple to implement since they are calibrated to the correct size of 32x32px (Sorry I have no way of testing discussion on my machine at the moment).

![hover-show-more](https://f.cloud.github.com/assets/85783/2076009/508c22b8-8d99-11e3-9826-7eed49b4d0d5.gif)

![ ](http://4.bp.blogspot.com/-lv45-8ns4NQ/Uu_VSNQflAI/AAAAAAABFvA/hadBec7abic/s1600/Driver-Parks-Perfectly-After-Losing-Control-of-Car.gif)