Video profiles

This change shares the profile for both the video player and the video's poster urls (there are two posters, one for html and one for flash). It means we get the right aspect ratio (no poster borders), and the right sized poster. It makes the upgrade to videojs less noticeable, because the poster image is consistent.

It's 16:9 in most places, with the exception of 'very big/ fromage' items, which are 5:3.

@robertberry @mattosborn 

**HTML examples (Before, borders everywhere)**
*Huge item*
![screen shot 2014-08-14 at 11 50 52](https://cloud.githubusercontent.com/assets/4549425/3918966/19eef368-23a1-11e4-8d00-982af59808e1.png)
*Boosted Very Big item, and two boosted big items*
![screen shot 2014-08-14 at 11 50 59](https://cloud.githubusercontent.com/assets/4549425/3918967/1cd5e744-23a1-11e4-9115-a79430ba276c.png)
*Boosted standard item*
![screen shot 2014-08-14 at 11 51 08](https://cloud.githubusercontent.com/assets/4549425/3918968/1ebb80a0-23a1-11e4-8b6c-417a91780833.png)
**HTML examples (After, no borders, same image as video js)**
*Huge item*
![screen shot 2014-08-14 at 11 46 13](https://cloud.githubusercontent.com/assets/4549425/3918913/81b98e32-23a0-11e4-91e3-720c7a91f29a.png)
*Boosted Very Big item, and two boosted big items*
![screen shot 2014-08-14 at 11 46 30](https://cloud.githubusercontent.com/assets/4549425/3918915/85820616-23a0-11e4-8382-33a4f3cd9095.png)
*Boosted standard item*
![screen shot 2014-08-14 at 11 46 37](https://cloud.githubusercontent.com/assets/4549425/3918917/8a22fd60-23a0-11e4-98e7-508af12e2115.png)
This `get` is on a Some, not an Option. See `VideoProfile`in images.scala (which I will change to a better filename)