Added history tracking to InheritanceGroup

`django-simple-history` doesn't currently track changes to many-to-many relationships - which was the main point of this commit
(i.e. to track the changes to `own_permissions`) - but once jazzband/django-simple-history#399 is resolved
(likely through jazzband/django-simple-history#932), it will.

groups/admin.py

@@ -5,7 +5,7 @@
 from .models import Committee, InheritanceGroup
 
 
-class InheritanceGroupAdmin(admin.ModelAdmin):
+class InheritanceGroupAdmin(SimpleHistoryAdmin):
     list_display = ('name', 'last_modified')
 
     fieldsets = (

groups/migrations/0011_historicalinheritancegroup.py

@@ -0,0 +1,36 @@
+# Generated by Django 4.0.3 on 2022-04-04 19:12
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+import simple_history.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('groups', '0010_alter_committee_image_filename'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='HistoricalInheritanceGroup',
+            fields=[
+                ('group_ptr', models.ForeignKey(auto_created=True, blank=True, db_constraint=False, null=True, on_delete=django.db.models.deletion.DO_NOTHING, parent_link=True, related_name='+', to='auth.group')),
+                ('id', models.IntegerField(auto_created=True, blank=True, db_index=True, verbose_name='ID')),
+                ('name', models.CharField(db_index=True, max_length=150, verbose_name='name')),
+                ('history_id', models.AutoField(primary_key=True, serialize=False)),
+                ('history_date', models.DateTimeField()),
+                ('history_change_reason', models.CharField(max_length=100, null=True)),
+                ('history_type', models.CharField(choices=[('+', 'Created'), ('~', 'Changed'), ('-', 'Deleted')], max_length=1)),
+                ('history_user', models.ForeignKey(null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='+', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'historical inheritance group',
+                'ordering': ('-history_date', '-history_id'),
+                'get_latest_by': 'history_date',
+            },
+            bases=(simple_history.models.HistoricalChanges, models.Model),
+        ),
+    ]

groups/models.py

@@ -37,6 +37,8 @@ class InheritanceGroup(Group):
     )
     last_modified = models.DateTimeField(auto_now=True, verbose_name=_("last modified"))
 
+    history = HistoricalRecords(excluded_fields=['last_modified'])
+
     @property
     def inherited_permissions(self):
         return set(self.permissions.all()) - set(self.own_permissions.all())