Open cta squash

# What?

The open CTA in the right hand side, when populated with a comment has the problem of, on occasion, being **massive**.

We have added a line-clamp to it, with a `read more` CTA.

# Looky

### Before
![open-cta-read-more-massive](https://f.cloud.github.com/assets/31692/1672762/a3a3772c-5cd8-11e3-9c57-45fbaf25a484.png)

### After
![top-comment-read-more](https://f.cloud.github.com/assets/31692/1672755/8806e5f8-5cd8-11e3-8f76-f2831ed78d3f.png)

# Notes
* clamp.js has been done as a very simple plugin. [There are other options](https://github.com/josephschmitt/Clamp.js/blob/master/clamp.js), but they come with lots of polyfiller we don't need. If this becomes more useful, we can steal what we need from elsewhere and use our own Microlibs.