implement mail address target editing

- extract common code into managemails.forms.MailAddressFieldMixin
- move code from forms into managemails.models.MailAddress
- implement managemails.models.MailboxManager.unused and unused_or_own
- implement managemails.forms.EditMailAddressForm
- add managemails.views.EditMailAddress
- add URL pattern 'edit_mailaddress' to managemails.urls
- add template managemails/mailaddress_edit.html
- add changelog entry

gnuviechadmin/templates/managemails/mailaddress_edit.html

@@ -0,0 +1,26 @@
+{% extends "managemails/base.html" %}
+{% load i18n crispy_forms_tags %}
+
+{% block title %}{{ block.super }} - {% spaceless %}
+{% if user == customer %}
+{% blocktrans %}Change target of Mail Address{% endblocktrans %}
+{% else %}
+{% blocktrans with full_name=customer.get_full_name %}
+Change target of Mail Address for Customer {{ full_name }}
+{% endblocktrans %}
+{% endif %}
+{% endspaceless %}{% endblock title %}
+
+{% block page_title %}{% spaceless %}
+{% if user == customer %}
+{% blocktrans %}Change target of Mail Address{% endblocktrans %}
+{% else %}
+{% blocktrans with full_name=customer.get_full_name %}
+Change target of Mail Address for Customer {{ full_name }}
+{% endblocktrans %}
+{% endif %}
+{% endspaceless %}{% endblock page_title %}
+
+{% block content %}
+{% crispy form %}
+{% endblock content %}