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/serializers.py

@@ -1,6 +1,10 @@
 from rest_framework import serializers
-from bookshelf.models import Book, Author, Publisher
-from metadata.serializers import TagSerializer
+from bookshelf.models import Book, Catalog, Author, Publisher
+from metadata.serializers import (
+    ScaleSerializer,
+    ManufacturerSerializer,
+    TagSerializer
+)
 
 
 class AuthorSerializer(serializers.ModelSerializer):
@@ -22,5 +26,16 @@ class BookSerializer(serializers.ModelSerializer):
 
     class Meta:
         model = Book
-        fields = "__all__"
+        exclude = ("price",)
+        read_only_fields = ("creation_time", "updated_time")
+
+
+class CatalogSerializer(serializers.ModelSerializer):
+    scales = ScaleSerializer(many=True)
+    manufacturer = ManufacturerSerializer()
+    tags = TagSerializer(many=True)
+
+    class Meta:
+        model = Catalog
+        exclude = ("price",)
         read_only_fields = ("creation_time", "updated_time")