Download Support (#298)

* Implemented the ability to download files (series, volume, chapter)

* Added RBS checks to ensure user is either an admin or has download role

* Added the ability to change a users feature RBS. Changed the Role seed to use reflection

API/Constants/PolicyConstants.cs

@@ -4,5 +4,9 @@
     {
         public const string AdminRole = "Admin";
         public const string PlebRole = "Pleb";
+        /// <summary>
+        /// Used to give a user ability to download files from the server
+        /// </summary>
+        public const string DownloadRole = "Download";
     }
 }