Added property display: flex and none

Summary:
Fix #241 and successor for #302

Added new property ```display``` with ```YGDisplayFlex``` and ```YGDisplayNone```. Allows to hide nodes from the layout without the need to remove it from the DOM.
Closes https://github.com/facebook/yoga/pull/369

Reviewed By: astreet

Differential Revision: D4501141

Pulled By: emilsjolander

fbshipit-source-id: 0dfeee381f6d1e4bbba81926126b83dd7abab9d6

yoga/YGEnums.h

@@ -36,6 +36,12 @@ typedef YG_ENUM_BEGIN(YGDirection) {
   YGDirectionRTL,
 } YG_ENUM_END(YGDirection);
 
+#define YGDisplayCount 2
+typedef YG_ENUM_BEGIN(YGDisplay) {
+  YGDisplayFlex,
+  YGDisplayNone,
+} YG_ENUM_END(YGDisplay);
+
 #define YGEdgeCount 9
 typedef YG_ENUM_BEGIN(YGEdge) {
   YGEdgeLeft,