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

javascript/sources/YGEnums.js

@@ -26,6 +26,10 @@ module.exports = {
   DIRECTION_LTR: 1,
   DIRECTION_RTL: 2,
 
+  DISPLAY_COUNT: 2,
+  DISPLAY_FLEX: 0,
+  DISPLAY_NONE: 1,
+
   EDGE_COUNT: 9,
   EDGE_LEFT: 0,
   EDGE_TOP: 1,