Minor admin improvements and remove unique_together deprecated Meta

Also make rolling stock unique per consist

ram/roster/migrations/0031_alter_rollingstockdocument_unique_together_and_more.py

@@ -0,0 +1,23 @@
+# Generated by Django 5.1.4 on 2025-01-08 22:22
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("roster", "0030_rollingstock_price"),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name="rollingstockdocument",
+            unique_together=set(),
+        ),
+        migrations.AddConstraint(
+            model_name="rollingstockdocument",
+            constraint=models.UniqueConstraint(
+                fields=("rolling_stock", "file"), name="unique_stock_file"
+            ),
+        ),
+    ]