Feature label styling (#454)

* Added some basic tests for the ECS

* Add test project for Nuclex Gui

* Nuclex Gui project update

* Added ability to style labels

* Removed Nuclex Gui Test project for lack of tests

Source/Tests/MonoGame.Extended.Entities.Tests/Implementation/EntityTemplateUsingManager.cs

@@ -0,0 +1,16 @@
+using MonoGame.Extended.Entities;
+
+namespace MonoGame.Extended.Gui.Tests.Implementation
+{
+    [EntityTemplate(Name)]
+    public class EntityTemplateUsingManager : EntityTemplate
+    {
+        public const string Name = nameof(EntityTemplateUsingManager);
+
+        protected override void Build(Entity entity)
+        {
+            var num = Manager.EntityManager.TotalEntitiesCount;
+            entity.Attach<EntityComponentBasic>(c => c.Number = num);
+        }
+    }
+}