Adding media tile pattern

@DoSomething/front-end 

Hey - I'm not ready to merge this in, but wanted to get some eyes on it to see if I am headed in the right direction. Also to start getting some feedback on code style practices here. Let me know if I'm on the right track!

This adds a new "Media Tile" pattern to neue that looks like the tiles in the gallery duo pattern. I think the next step would be to refactor the gallery duo pattern so that it just serves as a wrapper for any tile that is put in it, much like the other gallery patterns. 

Cheers :wine_glass: