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

csharp/Facebook.Yoga/Native.cs

@@ -169,6 +169,12 @@ namespace Facebook.Yoga
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern YogaOverflow YGNodeStyleGetOverflow(YGNodeHandle node);
 
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void YGNodeStyleSetDisplay(YGNodeHandle node, YogaDisplay display);
+
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern YogaDisplay YGNodeStyleGetDisplay(YGNodeHandle node);
+
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern void YGNodeStyleSetFlex(YGNodeHandle node, float flex);
 

csharp/Facebook.Yoga/YogaDisplay.cs

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+namespace Facebook.Yoga
+{
+    public enum YogaDisplay
+    {
+        Flex,
+        None,
+    }
+}

csharp/Facebook.Yoga/YogaNode.cs

@@ -145,6 +145,19 @@ namespace Facebook.Yoga
             }
         }
 
+        public YogaDisplay Display
+        {
+            get
+            {
+                return Native.YGNodeStyleGetDisplay(_ygNode);
+            }
+
+            set
+            {
+                Native.YGNodeStyleSetDisplay(_ygNode, value);
+            }
+        }
+
         public YogaAlign AlignItems
         {
             get