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/apps.py

@@ -0,0 +1,17 @@
+"""
+This module contains the :py:class:`django.apps.AppConfig` instance for the
+:py:mod:`managemails` app.
+
+"""
+from __future__ import unicode_literals
+from django.apps import AppConfig
+from django.utils.translation import ugettext_lazy as _
+
+
+class ManageMailsAppConfig(AppConfig):
+    """
+    AppConfig for the :py:mod:`managemails` app.
+
+    """
+    name = 'managemails'
+    verbose_name = _('Mailboxes and Mail Addresses')