improve managemails app

- add managemails.apps to give a more meaningful title in the admin site
- add verbose names to MailAddressMailbox fields
- implement managemails.models.Mailbox.get_mailaddresses and a corresponding
  property mailaddresses

gnuviechadmin/managemails/migrations/0003_auto_20150124_2029.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('managemails', '0002_auto_20150117_1238'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='mailaddressmailbox',
+            name='mailaddress',
+            field=models.OneToOneField(primary_key=True, serialize=False, to='managemails.MailAddress', verbose_name='mailaddress'),
+            preserve_default=True,
+        ),
+        migrations.AlterField(
+            model_name='mailaddressmailbox',
+            name='mailbox',
+            field=models.ForeignKey(verbose_name='mailbox', to='managemails.Mailbox'),
+            preserve_default=True,
+        ),
+    ]