Clean up some doc comments

MediaBrowser.Controller/Providers/IExternalId.cs

@@ -3,7 +3,9 @@ using MediaBrowser.Model.Providers;
 
 namespace MediaBrowser.Controller.Providers
 {
-    /// <summary>Represents and identifier for an external provider.</summary>
+    /// <summary>
+    /// Represents an identifier for an external provider.
+    /// </summary>
     public interface IExternalId
     {
         /// <summary>
@@ -14,11 +16,12 @@ namespace MediaBrowser.Controller.Providers
         /// <summary>
         /// Gets the unique key to distinguish this provider/type pair. This should be unique across providers.
         /// </summary>
-        // TODO: This property is not actually unique at the moment. It should be updated to be unique.
+        // TODO: This property is not actually unique across the concrete types at the moment. It should be updated to be unique.
         string Key { get; }
 
         /// <summary>
-        /// Gets the specific media type for this id.
+        /// Gets the specific media type for this id. This is used to distinguish between the different
+        /// external id types for providers with multiple ids.
         /// </summary>
         /// <remarks>
         /// This can be used along with the <see cref="Name"/> to localize the external id on the client.

MediaBrowser.Model/Providers/ExternalIdInfo.cs

@@ -13,10 +13,12 @@ namespace MediaBrowser.Model.Providers
         /// <summary>
         /// Gets or sets the unique key for this id. This key should be unique across all providers.
         /// </summary>
+        // TODO: This property is not actually unique across the concrete types at the moment. It should be updated to be unique.
         public string Key { get; set; }
 
         /// <summary>
-        /// Gets or sets the specific media type for this id.
+        /// Gets or sets the specific media type for this id. This is used to distinguish between the different
+        /// external id types for providers with multiple ids.
         /// </summary>
         /// <remarks>
         /// This can be used along with the <see cref="Name"/> to localize the external id on the client.

MediaBrowser.Model/Providers/ExternalIdMediaType.cs

@@ -1,16 +1,16 @@
 namespace MediaBrowser.Model.Providers
 {
     /// <summary>
-    /// The specific media type of an <see cref="IExternalId"/>.
+    /// The specific media type of an <see cref="ExternalIdInfo"/>.
     /// </summary>
     /// <remarks>
-    /// This is used as a translation key for clients.
+    /// Client applications may use this as a translation key.
     /// </remarks>
     public enum ExternalIdMediaType
     {
         /// <summary>
-        /// There is no specific media type associated with the external id, or the external provider only has one
-        /// id type so there is no need to be specific.
+        /// There is no specific media type associated with the external id, or this is the default id for the external
+        /// provider so there is no need to specify a type.
         /// </summary>
         General,