Add widget support to SourceColumn

Allow passing a widget class to SourceColumn. This makes
using lambdas to render model column unnecesary and are
mostly removed too.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/documents/views/document_views.py

@@ -20,7 +20,6 @@ from mayan.apps.common.generics import (
     SingleObjectDownloadView, SingleObjectEditView, SingleObjectListView
 )
 from mayan.apps.common.mixins import MultipleInstanceActionMixin
-from mayan.apps.common.utils import encapsulate
 from mayan.apps.converter.models import Transformation
 from mayan.apps.converter.permissions import (
     permission_transformation_delete, permission_transformation_edit
@@ -259,12 +258,7 @@ class DocumentDuplicatesListView(DocumentListView):
         return context
 
     def get_object_list(self):
-        try:
-            return DuplicatedDocument.objects.get(
-                document=self.get_document()
-            ).documents.all()
-        except DuplicatedDocument.DoesNotExist:
-            return Document.objects.none()
+        return self.get_document().get_duplicates()
 
 
 class DocumentEditView(SingleObjectEditView):
@@ -842,16 +836,6 @@ class DuplicatedDocumentListView(DocumentListView):
         context = super(DuplicatedDocumentListView, self).get_extra_context()
         context.update(
             {
-                'extra_columns': (
-                    {
-                        'name': _('Duplicates'),
-                        'attribute': encapsulate(
-                            lambda document: DuplicatedDocument.objects.get(
-                                document=document
-                            ).documents.count()
-                        )
-                    },
-                ),
                 'no_results_icon': icon_duplicated_document_list,
                 'no_results_text': _(
                     'Duplicates are documents that are composed of the exact '