Add a CSV export functionality in admin and add price fields (#41)

* Implement an action do download data in csv
* Refactor CSV download
* Move price to main models and add csv to bookshelf
* Update template and API
* Small refactoring

ram/bookshelf/migrations/0019_basebook_price.py

@@ -0,0 +1,36 @@
+# Generated by Django 5.1.4 on 2024-12-29 17:06
+
+from django.db import migrations, models
+
+
+def price_to_property(apps, schema_editor):
+    basebook = apps.get_model("bookshelf", "BaseBook")
+    for row in basebook.objects.all():
+        prop = row.property.filter(property__name__icontains="price")
+        for p in prop:
+            try:
+                row.price = float(p.value)
+            except ValueError:
+                pass
+        row.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookshelf", "0018_alter_basebookdocument_options"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="basebook",
+            name="price",
+            field=models.DecimalField(
+                blank=True, decimal_places=2, max_digits=10, null=True
+            ),
+        ),
+        migrations.RunPython(
+            price_to_property,
+            reverse_code=migrations.RunPython.noop
+        ),
+    ]