Refactored all UserManager db access methods

Fixed stale cached entities in UserManager
Fixed wrong state persisting though method calls

MediaBrowser.Controller/Library/IUserManager.cs

@@ -24,14 +24,14 @@ namespace MediaBrowser.Controller.Library
         /// <summary>
         /// Gets the users.
         /// </summary>
-        /// <value>The users.</value>
-        IEnumerable<User> Users { get; }
+        /// <returns>The users.</returns>
+        IEnumerable<User> GetUsers();
 
         /// <summary>
         /// Gets the user ids.
         /// </summary>
-        /// <value>The users ids.</value>
-        IEnumerable<Guid> UsersIds { get; }
+        /// <returns>The users ids.</returns>
+        IEnumerable<Guid> GetUsersIds();
 
         /// <summary>
         /// Initializes the user manager and ensures that a user exists.
@@ -47,6 +47,12 @@ namespace MediaBrowser.Controller.Library
         /// <exception cref="ArgumentException"><c>id</c> is an empty Guid.</exception>
         User? GetUserById(Guid id);
 
+        /// <summary>
+        /// Gets the first available user.
+        /// </summary>
+        /// <returns>The first user, or <c>null</c> if no users exist.</returns>
+        User? GetFirstUser();
+
         /// <summary>
         /// Gets the name of the user by.
         /// </summary>
@@ -57,12 +63,13 @@ namespace MediaBrowser.Controller.Library
         /// <summary>
         /// Renames the user.
         /// </summary>
-        /// <param name="user">The user.</param>
+        /// <param name="userId">The UserId to change.</param>
+        /// <param name="oldName">The old Username.</param>
         /// <param name="newName">The new name.</param>
         /// <returns>Task.</returns>
         /// <exception cref="ArgumentNullException">If user is <c>null</c>.</exception>
         /// <exception cref="ArgumentException">If the provided user doesn't exist.</exception>
-        Task RenameUser(User user, string newName);
+        Task RenameUser(Guid userId, string oldName, string newName);
 
         /// <summary>
         /// Updates the user.