Copy affiliation data to incident targets

We are phasing out the one-affiliation-per-incident affiliation model
in favor of an Institution model, which can either be applied on a
journalist by journalist basis, or to the incident as a whole, but as
many as desired.

For this, we must move data from the legacy affiliation field to the
new Institution field.  We do this using a data migration, with two
pre- and post- migrations to work around this bug in
djang-modelcluster:
    wagtail/django-modelcluster#96

For the migration, we want these steps:

1. For each incident, examine the `affiliation` field

2. If it null or set to the default value of "Independent," discard
it.  The "independent" value is a placeholder for no definite
affiliation and will not be used in the new scheme.

3. Create, if it doesn't already exist, an Institution with the title
of the affiliation.

4. If this incident has any targeted journalists who do not already
have an associated institution, associate the new institution with
them.

5. If this incident does *not* have any targeted journalists, add the
new institution as a target of this incident.

This will fully bring any affiliation data into the institution model
and apply it to the incidents that this data described.

incident/migrations/0043_auto_20200306_1646.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.10 on 2020-03-06 16:46
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('incident', '0042_copy_uncategorized_targets_to_gov_workers'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='incidentpage',
+            name='targeted_institutions',
+            field=models.ManyToManyField(blank=True, related_name='institutions_incidents', to='incident.Institution', verbose_name='Targeted Institutions'),
+        ),
+    ]

incident/migrations/0044_copy_affiliation_to_institutions.py

@@ -0,0 +1,38 @@
+# Generated by Django 2.2.10 on 2020-03-05 21:28
+
+from django.db import migrations
+
+
+def copy_affiliation(apps, schema_editor):
+    """Copy incident affiliations to """
+    IncidentPage = apps.get_model('incident', 'IncidentPage')
+    Institution = apps.get_model('incident', 'Institution')
+
+    for incident in IncidentPage.objects.order_by('pk'):
+        if incident.affiliation and incident.affiliation != 'Independent':
+            inst, _ = Institution.objects.get_or_create(title=incident.affiliation)
+
+            targeted_journos = incident.targeted_journalists.all()
+            if targeted_journos:
+                for tj in targeted_journos:
+                    if not tj.institution:
+                        tj.institution = inst
+                        tj.save()
+            else:
+                incident.targeted_institutions.add(inst)
+                incident.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('incident', '0043_auto_20200306_1646'),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            copy_affiliation,
+            reverse_code=migrations.RunPython.noop,
+            elidable=True,
+        ),
+    ]

incident/migrations/0045_auto_20200306_1648.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.10 on 2020-03-06 16:48
+
+from django.db import migrations
+import modelcluster.fields
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('incident', '0044_copy_affiliation_to_institutions'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='incidentpage',
+            name='targeted_institutions',
+            field=modelcluster.fields.ParentalManyToManyField(blank=True, related_name='institutions_incidents', to='incident.Institution', verbose_name='Targeted Institutions'),
+        ),
+    ]