Resources loaded from the filesystem appear to have case sensitive na…

…mes - the default theme is named default.json (#192)

Vignette.Application/Configuration/ApplicationConfigManager.cs

@@ -17,7 +17,7 @@ public ApplicationConfigManager(Storage storage)
 
         protected override void InitialiseDefaults()
         {
-            SetValue(ApplicationSetting.Theme, @"Default");
+            SetValue(ApplicationSetting.Theme, @"default");
             SetValue(ApplicationSetting.WindowResizable, false);
             SetValue(ApplicationSetting.ShowFpsOverlay, false);
             SetValue(ApplicationSetting.Background, BackgroundType.Color);