Added initial implementation of the metadata provider network, along with the first few providers

MediaBrowser.Controller/Providers/BaseMetadataProvider.cs

@@ -0,0 +1,23 @@
+using System.Threading.Tasks;
+using MediaBrowser.Controller.Events;
+using MediaBrowser.Model.Entities;
+
+namespace MediaBrowser.Controller.Providers
+{
+    public abstract class BaseMetadataProvider
+    {
+        /// <summary>
+        /// If the provider needs any startup routines, add them here
+        /// </summary>
+        public virtual void Init()
+        {
+        }
+
+        public virtual bool Supports(BaseItem item)
+        {
+            return true;
+        }
+
+        public abstract Task Fetch(BaseItem item, ItemResolveEventArgs args);
+    }
+}