Ensure video as main media uses enhanced player and displays caption

- Use new markup for video-js player to enhance videos when in main media
- Get correct poster image
- Get caption

### Before
![google chrome](https://cloud.githubusercontent.com/assets/80089/3762585/a7d4ea2a-1898-11e4-8686-9aec03cf9b41.png)

### After 
![google chrome](https://cloud.githubusercontent.com/assets/80089/3762588/acab2eb0-1898-11e4-8b80-cd56282d9ed8.png)

/cc @rich-nguyen 
I think this is fine.