Move configuration to new YGConfig and pass them down to CalculateLayout

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

YogaKit/Source/YGLayout.m

@@ -85,6 +85,8 @@ YG_VALUE_EDGE_PROPERTY(lowercased_name##Horizontal, capitalized_name##Horizontal
 YG_VALUE_EDGE_PROPERTY(lowercased_name##Vertical, capitalized_name##Vertical, capitalized_name, YGEdgeVertical)       \
 YG_VALUE_EDGE_PROPERTY(lowercased_name, capitalized_name, capitalized_name, YGEdgeAll)
 
+static YGConfigRef globalConfig;
+
 @interface YGLayout ()
 
 @property (nonatomic, weak, readonly) UIView *view;
@@ -99,14 +101,15 @@ YG_VALUE_EDGE_PROPERTY(lowercased_name, capitalized_name, capitalized_name, YGEd
 
 + (void)initialize
 {
-  YGSetExperimentalFeatureEnabled(YGExperimentalFeatureWebFlexBasis, true);
+  globalConfig = YGConfigNew();
+  YGConfigSetExperimentalFeatureEnabled(globalConfig, YGExperimentalFeatureWebFlexBasis, true);
 }
 
 - (instancetype)initWithView:(UIView*)view
 {
   if (self = [super init]) {
     _view = view;
-    _node = YGNodeNew();
+    _node = YGNodeNewWithConfig(globalConfig);
     YGNodeSetContext(_node, (__bridge void *) view);
     _isEnabled = NO;
     _isIncludedInLayout = YES;