Migrate to GIF API

[andrewvy]

It would be cool to not hardcode some starting GIFs and just fetch random ones off the internet. :)

Not sure if there's any good GIF search APIs out there. Imgur's looks pretty bland.

[dblock]

@orta, care to point us to the code used by Gif App to search for GIFs?

[orta]

https://github.com/orta/GIFKit/blob/master/Pod/Classes/ORGiphyNetworkModel.m#L41

[dblock]

Also need to be able to request GIFs smaller than XX MB whatever the default slack limit is.

[orta]

You'll pretty reliably get the same results on giphy, so I'd recommend random paging + a few keywords to work from.