Add YogaKit Shared and iOS version

Summary:
Using shared code for reuse in other platforms based on iOS native implementation.

Adds YogaKit sample.

Adds YogaKit tests (same as objc).

```
YogaKitTest : 80 ms
Facebook.YogaKit.iOS.Tests.exe : 81 ms
Tests run: 11 Passed: 8 Inconclusive: 0 Failed: 3 Ignored: 1
```

Since we don't have extension properties we need to go with a extension method to get access to the YogaLayout .

I m also not sure this is leak free yet, would love some help with testing and feedback about view/node lifecycle
Closes https://github.com/facebook/yoga/pull/336

Reviewed By: splhack

Differential Revision: D4415027

Pulled By: emilsjolander

fbshipit-source-id: c88328212426c3200e6f0c48cda594cd2c432065

csharp/Facebook.YogaKit/IYogaLayout.cs

@@ -0,0 +1,85 @@
+using System;
+using System.Drawing;
+using Facebook.Yoga;
+
+namespace Facebook.YogaKit
+{
+	public interface IYogaLayout : IDisposable
+	{
+		bool IsEnabled { get; set; }
+		bool IsIncludeInLayout { get; set; }
+
+		//YogaDirection Direction { get; set; }
+		YogaFlexDirection FlexDirection { get; set; }
+		YogaJustify JustifyContent { get; set; }
+		YogaAlign AlignContent { get; set; }
+		YogaAlign AlignSelf { get; set; }
+		YogaAlign AlignItems { get; set; }
+		YogaPositionType Position { get; set; }
+		YogaWrap FlexWrap { get; set; }
+		YogaOverflow Overflow { get; set; }
+
+
+		float FlexGrow { get; set; }
+		float FlexShrink { get; set; }
+		float FlexBasis { get; set; }
+
+		float Left { get; set; }
+		float Top { get; set; }
+		float Right { get; set; }
+		float Bottom { get; set; }
+		float Start { get; set; }
+		float End { get; set; }
+
+		float MarginLeft { get; set; }
+		float MarginTop { get; set; }
+		float MarginRight { get; set; }
+		float MarginBottom { get; set; }
+		float MarginStart { get; set; }
+		float MarginEnd { get; set; }
+		float MarginHorizontal { get; set; }
+		float MarginVertical { get; set; }
+		float Margin { get; set; }
+
+		float PaddingLeft { get; set; }
+		float PaddingTop { get; set; }
+		float PaddingRight { get; set; }
+		float PaddingBottom { get; set; }
+		float PaddingStart { get; set; }
+		float PaddingEnd { get; set; }
+		float PaddingHorizontal { get; set; }
+		float PaddingVertical { get; set; }
+		float Padding { get; set; }
+
+		float BorderLeftWidth { get; set; }
+		float BorderTopWidth { get; set; }
+		float BorderRightWidth { get; set; }
+		float BorderBottomWidth { get; set; }
+		float BorderStartWidth { get; set; }
+		float BorderEndWidth { get; set; }
+		float BorderWidth { get; set; }
+
+		float Width { get; set; }
+		float Height { get; set; }
+		float MinWidth { get; set; }
+		float MinHeight { get; set; }
+		float MaxWidth { get; set; }
+		float MaxHeight { get; set; }
+
+		// Yoga specific properties, not compatible with flexbox specification
+
+		// Returns the size of the view if no constraints were given. This could equivalent to calling [self sizeThatFits:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)];
+		SizeF IntrinsicSize { get; }
+		float AspectRatio { get; set; }
+		// Get the resolved direction of this node. This won't be YGDirectionInherit
+		YogaDirection ResolvedDirection { get; }
+		// Returns the number of children that are using Flexbox.
+		int NumberOfChildren { get; }
+		// Return a BOOL indiciating whether or not we this node contains any subviews that are included in Yoga's layout.
+		bool IsLeaf { get; }
+		// Perform a layout calculation and update the frames of the views in the hierarchy with the results
+		void ApplyLayout();
+		// Mark that a view's layout needs to be recalculated. Only works for leaf views.
+		void MarkDirty();
+	}
+}