Use video captions

**From this:**
![screen shot 2014-08-21 at 12 18 29](https://cloud.githubusercontent.com/assets/4549425/3995248/370ad988-2925-11e4-9adc-e4e0e916e3d0.png)

**To this:**
![screen shot 2014-08-21 at 12 18 38](https://cloud.githubusercontent.com/assets/4549425/3995251/473d60be-2925-11e4-8f2f-c4013a1077e9.png)

@sihil 
In a true BEM world, I would prefer this it the classes where:
```css
caption caption--main caption--img
```

The `caption--main` would give it it's larger styling, and the `caption--img` modify to have image icon e.t.c.