Migrate from constance to dynamic-preferences

Rationale: django-dynamic-preferences allows defining global preferences and "instance preferences", i.e. user preferences, the same way. It is also way more sophisticated than constance and provides more possibilities for preference fields as well as rendering options.

Closes #162 (closed), advances #214 (closed) and others.

aleksis/core/migrations/0025_dynamic_preferences.py

+# Generated by Django 3.0.5 on 2020-04-30 19:41
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('sites', '0002_alter_domain_unique'),
+        ('core', '0024_globalpermissions'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='GroupPreferenceModel',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('section', models.CharField(blank=True, db_index=True, default=None, max_length=150, null=True, verbose_name='Section Name')),
+                ('name', models.CharField(db_index=True, max_length=150, verbose_name='Name')),
+                ('raw_value', models.TextField(blank=True, null=True, verbose_name='Raw Value')),
+            ],
+        ),
+        migrations.CreateModel(
+            name='PersonPreferenceModel',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('section', models.CharField(blank=True, db_index=True, default=None, max_length=150, null=True, verbose_name='Section Name')),
+                ('name', models.CharField(db_index=True, max_length=150, verbose_name='Name')),
+                ('raw_value', models.TextField(blank=True, null=True, verbose_name='Raw Value')),
+            ],
+        ),
+        migrations.CreateModel(
+            name='SitePreferenceModel',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('section', models.CharField(blank=True, db_index=True, default=None, max_length=150, null=True, verbose_name='Section Name')),
+                ('name', models.CharField(db_index=True, max_length=150, verbose_name='Name')),
+                ('raw_value', models.TextField(blank=True, null=True, verbose_name='Raw Value')),
+                ('instance', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='sites.Site')),
+            ],
+        ),
+        migrations.DeleteModel(
+            name='School',
+        ),
+        migrations.DeleteModel(
+            name='SchoolTerm',
+        ),
+        migrations.AlterModelOptions(
+            name='group',
+            options={'ordering': ['short_name', 'name'], 'permissions': (('assign_child_groups_to_groups', 'Can assign child groups to groups'),), 'verbose_name': 'Group', 'verbose_name_plural': 'Groups'},
+        ),
+        migrations.AlterModelOptions(
+            name='person',
+            options={'ordering': ['last_name', 'first_name'], 'permissions': (('view_address', 'Can view address'), ('view_contact_details', 'Can view contact details'), ('view_photo', 'Can view photo'), ('view_person_groups', 'Can view persons groups'), ('view_personal_details', 'Can view personal details')), 'verbose_name': 'Person', 'verbose_name_plural': 'Persons'},
+        ),
+        migrations.AddField(
+            model_name='personpreferencemodel',
+            name='instance',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='core.Person'),
+        ),
+        migrations.AddField(
+            model_name='grouppreferencemodel',
+            name='instance',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='core.Group'),
+        ),
+    ]