Adds jupyter notebook support

Forces the installation of django_extensions.

Simply adds the `shell_plus` command to be seen in main evennia binary when
parsing arguments.

A notebook can be started with the following

`evennia shell_plus --notebook`

evennia/server/evennia_launcher.py

@@ -2259,7 +2259,7 @@ def main():
         if option in ("makemessages", "compilemessages"):
             # some commands don't require the presence of a game directory to work
             need_gamedir = False
-        if option in ("shell", "check", "makemigrations", "createsuperuser"):
+        if option in ("shell", "check", "makemigrations", "createsuperuser", "shell_plus"):
             # some django commands requires the database to exist,
             # or evennia._init to have run before they work right.
             check_db = True

requirements.txt

@@ -8,6 +8,7 @@ pytz
 djangorestframework >= 3.10.3, < 3.12
 django-filter >= 2.2.0, < 2.3
 django-sekizai
+django-extensions >= 3.1.0
 inflect
 autobahn >= 17.9.3
 lunr == 0.5.6