Added escaped page source in Meta page

pages/models.py

 from django.conf import settings
 from django.contrib.auth.models import User, Group
 from django.db import models
+from django.utils.html import escape
 from django.utils.translation import gettext as _
 from simple_history.models import HistoricalRecords
 
         else:
             appendix = "<h1>" + _("Page source") + "</h1>\n"
             appendix += "<pre>\n"
-            appendix += self.page_txt
+            appendix += escape(self.page_txt)
             appendix += "</pre>\n"
 
         #