- added IsDisposed to form

- removed FormSwitched from FormBase and added to DeviceSession (more logical message loop)
- added PreviousForm to DeviceSession, contains last opened form (at initial form is null)
-BotBase message loop update
- now navigation is possible from every form, not just the latest ones as before

TelegramBotBase/Sessions/DeviceSession.cs

@@ -37,6 +37,16 @@ namespace TelegramBotBase.Sessions
         /// </summary>
         public FormBase ActiveForm { get; set; }
 
+        /// <summary>
+        /// Returns the previous shown form
+        /// </summary>
+        public FormBase PreviousForm { get; set; }
+
+        /// <summary>
+        /// contains if the form has been switched (navigated)
+        /// </summary>
+        public bool FormSwitched { get; set; } = false;
+
         /// <summary>
         /// Returns the ID of the last received message.
         /// </summary>