Add copy magnet link button in movie detail page

Added a small button aside the play button, for copying magnet link
into system clipboard. So that we might need to use the link in
somewhere ellse.

Following is the screenshot with the new button added:

![qq20140329-1](https://cloud.githubusercontent.com/assets/529486/2552360/48c9e1be-b698-11e3-8d7e-0c04ef9e4643.png)