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/IO/FileSystemProviderManager.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Linq;
+using System.Text;
+using Umbraco.Core.Configuration;
+
+namespace Umbraco.Core.IO
+{
+    internal class FileSystemProviderManager
+    {
+        private readonly FileSystemProvidersSection _config;
+
+        #region Singleton
+
+        private static readonly FileSystemProviderManager Instance = new FileSystemProviderManager();
+
+        public static FileSystemProviderManager Current
+        {
+            get { return Instance; }
+        }
+
+        #endregion
+
+        #region Constructors
+
+        public FileSystemProviderManager()
+        {
+            _config = (FileSystemProvidersSection)ConfigurationManager.GetSection("FileSystemProviders");
+        }
+
+        #endregion
+
+        public IFileSystem GetFileSystemProvider(string alias)
+        {
+            var providerConfig = _config.Providers[alias];
+            if(providerConfig == null)
+                throw new ArgumentException(string.Format("No provider found with the alias '{0}'", alias));
+
+            var providerType = Type.GetType(providerConfig.Type);
+            if(providerType == null)
+                throw new InvalidOperationException(string.Format("Could not find type '{0}'", providerConfig.Type));
+
+            if (providerType.IsAssignableFrom(typeof(IFileSystem)))
+                throw new InvalidOperationException(string.Format("The type '{0}' does not implement IFileSystem", providerConfig.Type));
+
+            var paramCount = providerConfig.Parameters != null ? providerConfig.Parameters.Count : 0;
+            var constructor = providerType.GetConstructors()
+                .SingleOrDefault(x => x.GetParameters().Count() == paramCount 
+                    && x.GetParameters().All(y => providerConfig.Parameters.AllKeys.Contains(y.Name)));
+            if(constructor == null)
+                throw new InvalidOperationException(string.Format("Could not find constructor for type '{0}' which accepts {1} parameters", providerConfig.Type, paramCount));
+
+            var parameters = new object[paramCount];
+            for(var i = 0; i < paramCount; i++)
+                parameters[i] = providerConfig.Parameters[providerConfig.Parameters.AllKeys[i]].Value;
+
+            return (IFileSystem) constructor.Invoke(parameters);
+        }
+    }
+}