Made config a singleton

Author: Alxandr

src/React.Sample.Mvc4/App_Start/ReactConfig.cs

@@ -15,7 +15,7 @@ public static class ReactConfig
 	{
 		public static void Configure()
 		{
-			ReactSiteConfiguration.Configuration = new ReactSiteConfiguration()
+			ReactSiteConfiguration.Configuration
 				.AddScript("~/Content/Sample.jsx");
 		}
 	}

src/React.Tests/Core/JsxTransformerTests.cs

@@ -40,7 +40,8 @@ public void SetUp()
 				_environment.Object,
 				_cache.Object,
 				_fileSystem.Object,
-				_fileCacheHash.Object
+				_fileCacheHash.Object,
+				ReactSiteConfiguration.Configuration
 			);
 		}
 

src/React/ReactSiteConfiguration.cs

@@ -17,6 +17,8 @@ namespace React
 	/// </summary>
 	public class ReactSiteConfiguration : IReactSiteConfiguration
 	{
+		private static IReactSiteConfiguration _instance = new ReactSiteConfiguration();
+
 		/// <summary>
 		/// All the scripts that have been added to this configuration
 		/// </summary>
@@ -25,7 +27,13 @@ public class ReactSiteConfiguration : IReactSiteConfiguration
 		/// <summary>
 		/// Gets or sets the site-side configuration
 		/// </summary>
-		public static IReactSiteConfiguration Configuration { get; set; }
+		public static IReactSiteConfiguration Configuration
+		{
+			get
+			{
+				return _instance;
+			}
+		}
 
 		/// <summary>
 		/// Adds a script to the list of scripts that are executed. This should be called for all