add preview_image field to admin post form in blog_ext app

blog_ext/forms.py

@@ -1,10 +1,30 @@
+from django.forms import forms
 from django.utils.translation import ugettext_lazy as _
 
 from pinax.blog.forms import AdminPostForm as BaseAdminPostForm
 
+from blog_ext.models import Post
+
+FIELDS = [
+    "section",
+    "author",
+    "preview_image",
+    "markup",
+    "title",
+    "slug",
+    "teaser",
+    "content",
+    "description",
+    "state"
+]
+
 
 class AdminPostForm(BaseAdminPostForm):
-    pass
+    preview_image = forms.FileField(label=_('Превью изображение'), allow_empty_file=True)
+
+    class Meta:
+        model = Post
+        fields = FIELDS
 
 
 AdminPostForm.declared_fields.get('teaser').label = _('Превью')