galaxy: big refactor

Main changes:
  - Multiple Galaxy objects can now exist at the same time in DB. This allows for ruling a new galaxy while still
    displaying the old one.
  - The criteria to quickly know whether a user is a possible citizen is now a simple query on picture count. This
    avoids a very complicated query to database, that could often result in huge working memory load. With this change,
    it should be possible to run the galaxy even on a vanilla Postgres that didn't receive fine tuning for the Sith's
    galaxy.

galaxy/migrations/0002_auto_20230412_1130.py

@@ -0,0 +1,45 @@
+# Generated by Django 3.2.16 on 2023-04-12 09:30
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ("galaxy", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="galaxy",
+            options={"ordering": ["pk"]},
+        ),
+        migrations.AddField(
+            model_name="galaxystar",
+            name="galaxy",
+            field=models.ForeignKey(
+                null=True,
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="stars",
+                to="galaxy.galaxy",
+                verbose_name="the galaxy this star belongs to",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="galaxy",
+            name="state",
+            field=models.JSONField(null=True, verbose_name="The galaxy current state"),
+        ),
+        migrations.AlterField(
+            model_name="galaxystar",
+            name="owner",
+            field=models.ForeignKey(
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="stars",
+                to=settings.AUTH_USER_MODEL,
+                verbose_name="star owner",
+            ),
+        ),
+    ]