Minor admin improvements and remove unique_together deprecated Meta

Also make rolling stock unique per consist

ram/consist/migrations/0014_alter_consistitem_order.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.1.4 on 2025-01-08 22:22
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("consist", "0013_consistitem_one_stock_per_consist"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="consistitem",
+            name="order",
+            field=models.PositiveIntegerField(default=1000),
+        ),
+    ]