fixing Hardcoded Non-Cryptographic Secret and change the port to 8080 .

- version : 2.6
- Details : adding .env file that has the secret key and use it .. using
  different python modules and removing the unused route `/add_lesson`.
//############################################//
	modified:   .gitignore
	modified:   app.py
	modified:   requirements.txt
	modified:   serve.sh
//############################################//

.gitignore

@@ -1,3 +1,4 @@
 __pycache__
 *.db
 databases
+.env