Fix bug on visiting a segment page in the admin

Wagtail's InlinePanel's relies on
django.db.models.options.Options.get_field -
bcf6b6da77/wagtail/admin/edit_handlers.py (L688)
which seems to have a bug of using related_query_name rather than
related_name naming and therefore trying to edit segment always
fails - https://code.djangoproject.com/ticket/29458. The bug has not
yet been confirmed by others but it's impossible to edit segments.

Therefore this change deletes related_query_name from relations from
rules to the Segment model.

src/wagtail_personalisation/migrations/0020_rules_delete_relatedqueryname.py

@@ -0,0 +1,50 @@
+# Generated by Django 2.0.5 on 2018-05-30 18:51
+
+from django.db import migrations
+import django.db.models.deletion
+import modelcluster.fields
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('wagtail_personalisation', '0019_auto_20180526_1425'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='dayrule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_dayrules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='devicerule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_devicerules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='queryrule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_queryrules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='referralrule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_referralrules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='timerule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_timerules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='userisloggedinrule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_userisloggedinrules', to='wagtail_personalisation.Segment'),
+        ),
+        migrations.AlterField(
+            model_name='visitcountrule',
+            name='segment',
+            field=modelcluster.fields.ParentalKey(on_delete=django.db.models.deletion.CASCADE, related_name='wagtail_personalisation_visitcountrules', to='wagtail_personalisation.Segment'),
+        ),
+    ]

src/wagtail_personalisation/models.py

@@ -121,7 +121,7 @@ class Segment(ClusterableModel):
             ], heading="Segment"),
             MultiFieldPanel([
                 InlinePanel(
-                    "{}_related".format(rule_model._meta.db_table),
+                    "{}s".format(rule_model._meta.db_table),
                     label='{}{}'.format(
                         rule_model._meta.verbose_name,
                         ' ({})'.format(_('Static compatible')) if rule_model.static else ''

src/wagtail_personalisation/rules.py

@@ -29,8 +29,7 @@ class AbstractBaseRule(models.Model):
 
     segment = ParentalKey(
         'wagtail_personalisation.Segment',
-        related_name="%(app_label)s_%(class)s_related",
-        related_query_name="%(app_label)s_%(class)ss"
+        related_name="%(app_label)s_%(class)ss",
     )
 
     class Meta: