Update MonoGame windows 8 store app project with IK classes.

spine-monogame/windows8-store/src/SpineMonogameWindows8Store.csproj

@@ -174,6 +174,12 @@
     <Compile Include="..\..\..\spine-csharp\src\EventData.cs">
       <Link>spine-csharp\EventData.cs</Link>
     </Compile>
+    <Compile Include="..\..\..\spine-csharp\src\IkConstraint.cs">
+      <Link>spine-csharp\IkConstraint.cs</Link>
+    </Compile>
+    <Compile Include="..\..\..\spine-csharp\src\IkConstraintData.cs">
+      <Link>spine-csharp\IkConstraintData.cs</Link>
+    </Compile>
     <Compile Include="..\..\..\spine-csharp\src\Json.cs">
       <Link>spine-csharp\Json.cs</Link>
     </Compile>