personal: Move Group class definition before Contact

We want to reference Group from Contact in the following commit, so move
the class in the source file.

mpicms/personal/models.py

@@ -91,6 +91,34 @@ def __str__(self):
     class Meta:
         ordering = ["title"]
 
+
+@register_snippet
+class Group(index.Indexed, ClusterableModel):
+    slug = models.CharField(_("slug"), max_length=254)
+    name = models.CharField(_("name"), max_length=254, blank=True)
+    priority = models.PositiveSmallIntegerField(
+        _("priority"), blank=True, default=0, validators=[MaxValueValidator(99)],
+        help_text=_("Priority from 0-99 to determine the sorting order."))
+
+    panels = [
+        FieldPanel('name'),
+        FieldPanel('priority'),
+    ]
+
+    search_fields = [
+        index.SearchField('name', partial_match=True),
+        index.SearchField('slug'),
+    ]
+
+    def __str__(self):
+        return self.name or self.slug
+
+    class Meta:  # noqa
+        verbose_name = 'Group'
+        verbose_name_plural = 'Groups'
+        ordering = ['name']
+
+
 @register_snippet
 class Contact(index.Indexed, ClusterableModel):
     """
@@ -168,33 +196,6 @@ class Meta:  # noqa
         ordering = ['last_name']
 
 
-@register_snippet
-class Group(index.Indexed, ClusterableModel):
-    slug = models.CharField(_("slug"), max_length=254)
-    name = models.CharField(_("name"), max_length=254, blank=True)
-    priority = models.PositiveSmallIntegerField(
-        _("priority"), blank=True, default=0, validators=[MaxValueValidator(99)],
-        help_text=_("Priority from 0-99 to determine the sorting order."))
-
-    panels = [
-        FieldPanel('name'),
-        FieldPanel('priority'),
-    ]
-
-    search_fields = [
-        index.SearchField('name', partial_match=True),
-        index.SearchField('slug'),
-    ]
-
-    def __str__(self):
-        return self.name or self.slug
-
-    class Meta:  # noqa
-        verbose_name = 'Group'
-        verbose_name_plural = 'Groups'
-        ordering = ['name']
-
-
 class WrittenConsent(models.Model):
     ref = models.CharField("ID", max_length=10, unique=True)
     comment = models.TextField("comment", blank=True)