Summary:
Move configuration to new ```YGConfig``` and pass them down to CalculateLayout. See #418 .
Adds ```YGConfigNew()``` + ```YGConfigFree```, and changed ```YGSetExperimentalFeatureEnabled``` to use the config.
New function for calculation is ```YGNodeCalculateLayoutWithConfig```.
Closes https://github.com/facebook/yoga/pull/432
Reviewed By: astreet
Differential Revision: D4611359
Pulled By: emilsjolander
fbshipit-source-id: a1332f0e1b21cec02129dd021ee57408449e10b0