Add download button to retrieve the torrent file

Hello, I added a download button next to the Watch one to be able to download the torrent file.
Here is a screen of the new UI :
![ui-with-download](https://f.cloud.github.com/assets/1064129/2480669/8a472f9e-b0c5-11e3-9daf-66b8894692b9.png)

I needed to add a 'download' entry to the translation file, but I'm not sure I had to push it too (as translations should go into the translations branch).