Added FileSystemProviders config section

Added FileSystemProviderManager class for fetching a file system provider by alias (this should probably be moved into the Umbraco context in 4.10)

src/Umbraco.Core/Configuration/FileSystemProviderElementCollection.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Linq;
+using System.Text;
+
+namespace Umbraco.Core.Configuration
+{
+    [ConfigurationCollection(typeof(FileSystemProviderElement), AddItemName = "Provider")]
+    public class FileSystemProviderElementCollection : ConfigurationElementCollection   
+    {
+        protected override ConfigurationElement CreateNewElement()
+        {
+            return new FileSystemProviderElement();
+        }
+
+        protected override object GetElementKey(ConfigurationElement element)
+        {
+            return ((FileSystemProviderElement)(element)).Alias;
+        }
+
+        new public FileSystemProviderElement this[string key]
+        {
+            get
+            {
+                return (FileSystemProviderElement)BaseGet(key);
+            }
+        }
+    }
+}