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/mailer/apps.py

@@ -53,30 +53,16 @@ class MailerApp(MayanAppConfig):
 
         MailerBackend.initialize()
 
+        SourceColumn(attribute='datetime', source=LogEntry)
+        SourceColumn(attribute='message', source=LogEntry)
+        SourceColumn(attribute='label', is_identifier=True, source=UserMailer)
         SourceColumn(
-            source=LogEntry, label=_('Date and time'), attribute='datetime'
+            attribute='default', source=UserMailer, widget=TwoStateWidget
         )
         SourceColumn(
-            source=LogEntry, label=_('Message'), attribute='message'
-        )
-        SourceColumn(
-            source=UserMailer, label=_('Label'), attribute='label'
-        )
-        SourceColumn(
-            source=UserMailer, label=_('Default?'),
-            func=lambda context: TwoStateWidget(
-                state=context['object'].default
-            ).render()
-        )
-        SourceColumn(
-            source=UserMailer, label=_('Enabled?'),
-            func=lambda context: TwoStateWidget(
-                state=context['object'].enabled
-            ).render()
-        )
-        SourceColumn(
-            source=UserMailer, label=_('Label'), attribute='backend_label'
+            attribute='enabled', source=UserMailer, widget=TwoStateWidget
         )
+        SourceColumn(attribute='backend_label', source=UserMailer)
 
         ModelPermission.register(
             model=Document, permissions=(

mayan/apps/mailer/models.py

@@ -20,7 +20,7 @@ logger = logging.getLogger(__name__)
 
 class LogEntry(models.Model):
     datetime = models.DateTimeField(
-        auto_now_add=True, editable=False, verbose_name=_('Date time')
+        auto_now_add=True, editable=False, verbose_name=_('Date and time')
     )
     message = models.TextField(
         blank=True, editable=False, verbose_name=_('Message')
@@ -76,6 +76,7 @@ class UserMailer(models.Model):
         property.
         """
         return self.get_backend().label
+    backend_label.short_description = _('Backend label')
 
     def dumps(self, data):
         """