Add user permission checks for series editing and enhance author display method

generic/models.py

@@ -387,7 +387,7 @@ class SeriesImageBase(models.Model):
         super().save(*args, **kwargs)  # Call the "real" save() method.
 
 
-class SeriesBase(models.Model):
+class SeriesBase(models.Model, AuthorMixin):
     info = models.TextField(
         blank=True,
         help_text="Description of stack, for admin organisation, will not be visible when taking",
@@ -444,16 +444,6 @@ class SeriesBase(models.Model):
 
         return False
 
-    def get_author_objects(self):
-        """Returns a list of authors"""
-        if self.author:
-            return self.author.all()
-        else:
-            return ["None"]
-
-    def get_author_display(self):
-        return ", ".join([i.username for i in self.get_author_objects()])
-
     def get_examination(self):
         """Returns a comma seperated text list of regions"""
         return str(self.examination)