Summary:
To date, our sample project was lacking. There is still a lot of work that can be done to improve, but, this is a step in the right direction.
Here are the changes in this commit:
1. The project is written in Swift.
2. Created new CollectionView (via [IGListKit](https://github.com/instagram/iglistkit)), making it very easy to add new examples.
3. New examples for basic layouts, and including/excluding layouts on the fly.
Here's a video!

Closes https://github.com/facebook/yoga/pull/392
Reviewed By: emilsjolander
Differential Revision: D4550379
Pulled By: dshahidehpour
fbshipit-source-id: 64a07acf96c1887f1d2ad0c54971fcedb64334a0
Summary: The Sample app needed some love. It wouldn't build because of some import errors, adding files is very manual, and it looked bad. I have fixed all of these things.
Reviewed By: amonshiz
Differential Revision: D4508624
fbshipit-source-id: bda40defb167ef871d8d0d5bb853d8905b9682d8