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

gentest/gentest-cpp.js

@@ -118,6 +118,9 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
 
   YGUndefined:{value:'YGUndefined'},
 
+  YGDisplayFlex:{value:'YGDisplayFlex'},
+  YGDisplayNone:{value:'YGDisplayNone'},
+
   YGNodeCalculateLayout:{value:function(node, dir) {
     this.push('YGNodeCalculateLayout(' + node + ', YGUndefined, YGUndefined, ' + dir + ');');
   }},
@@ -162,6 +165,10 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
     this.push('YGNodeStyleSetDirection(' + nodeName + ', ' + toValueCpp(value) + ');');
   }},
 
+  YGNodeStyleSetDisplay:{value:function(nodeName, value) {
+    this.push('YGNodeStyleSetDisplay(' + nodeName + ', ' + toValueCpp(value) + ');');
+  }},
+
   YGNodeStyleSetFlexBasis:{value:function(nodeName, value) {
     this.push('YGNodeStyleSetFlexBasis' + toFunctionName(value) + '(' + nodeName + ', ' + toValueCpp(value) + ');');
   }},