Merge language and theme into resource folder

Wox.Core/Resource/ThemeManager.cs

@@ -0,0 +1,26 @@
+namespace Wox.Core.Resource
+{
+    public class ThemeManager
+    {
+        private static Theme instance;
+        private static object syncObject = new object();
+
+        public static Theme Theme
+        {
+            get
+            {
+                if (instance == null)
+                {
+                    lock (syncObject)
+                    {
+                        if (instance == null)
+                        {
+                            instance = new Theme();
+                        }
+                    }
+                }
+                return instance;
+            }
+        }
+    }
+}