Changing BotBase behaviour to fluent api

- removing unecessary constructors from BotBase
- removing generics from BotBase
- removing generics from SessionBase
- adding StartFormFactory interface
- adding DefaultStartFormFactory
- adding multiple methods to BotBaseBuilder

TelegramBotBase/Interfaces/IStartFormFactory.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using TelegramBotBase.Form;
+
+namespace TelegramBotBase.Interfaces
+{
+    public interface IStartFormFactory
+    {
+        FormBase CreateForm();
+    }
+}