Add email templates for user notifications and account management

- Created a base email template (base.html) for consistent styling across all emails.
- Added moderation approval email template (moderation_approved.html) to notify users of approved submissions.
- Added moderation rejection email template (moderation_rejected.html) to inform users of required changes for their submissions.
- Created password reset email template (password_reset.html) for users requesting to reset their passwords.
- Developed a welcome email template (welcome.html) to greet new users and provide account details and tips for using ThrillWiki.

django/apps/entities/apps.py

@@ -9,3 +9,7 @@ class EntitiesConfig(AppConfig):
     default_auto_field = 'django.db.models.BigAutoField'
     name = 'apps.entities'
     verbose_name = 'Entities'
+    
+    def ready(self):
+        """Import signal handlers when app is ready."""
+        import apps.entities.signals  # noqa