Adds New "What is Dogecoin" Video.

This Pull Request adds the "What is Dogecoin" YouTube video by /u/hfn64 on Reddit.
The method used to show this Dogecoin video is the same as the original, former design.
YouTube Video: https://www.youtube.com/watch?v=_KVZmS_UO5I

How it looks: http://i.imgur.com/5tapL0L.png
On button press: http://i.imgur.com/B8a0wZy.png