Rename DependencyInjection into DI, cleanup components, compose

src/Umbraco.Core/Components/RuntimeLevelAttribute.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Umbraco.Core.Components
+{
+    [AttributeUsage(AttributeTargets.Class /*, AllowMultiple = false, Inherited = true*/)]
+    public class RuntimeLevelAttribute : Attribute
+    {
+        //public RuntimeLevelAttribute()
+        //{ }
+
+        public RuntimeLevel MinLevel { get; set; } = RuntimeLevel.Boot;
+    }
+}