Add a 404 page and improve manufacturer lookup (#36)

* Add a custom 404 page
* Better manufacturer and item lookup
* Add migration to populate new field
* Version bump

ram/roster/migrations/0026_rollingstock_item_number_slug.py

@@ -0,0 +1,31 @@
+# Generated by Django 5.0.4 on 2024-04-23 21:10
+
+from django.db import migrations, models
+from ram.utils import slugify
+
+
+def gen_item_number_slug(apps, schema_editor):
+    RollingStock = apps.get_model('roster', 'RollingStock')
+    for row in RollingStock.objects.all():
+        if row.item_number:
+            row.item_number_slug = slugify(row.item_number)
+            row.save(update_fields=['item_number_slug'])
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("roster", "0025_rollingstock_set_alter_rollingstock_era_and_more"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="rollingstock",
+            name="item_number_slug",
+            field=models.CharField(blank=True, editable=False, max_length=32),
+        ),
+        migrations.RunPython(
+            gen_item_number_slug,
+            reverse_code=migrations.RunPython.noop
+        ),
+    ]