enable mailbox creation

- add managemails.urls to gnuviechadmin.urls
- add link to create_mailbox to customerhostingpackage_detail.html template
- document feature in changelog

gnuviechadmin/gnuviechadmin/urls.py

@@ -12,6 +12,7 @@ urlpatterns = patterns(
     url(r'^accounts/', include('allauth.urls')),
     url(r'^domains/', include('domains.urls')),
     url(r'^hosting/', include('hostingpackages.urls')),
+    url(r'^mail/', include('managemails.urls')),
     url(r'^osuser/', include('osusers.urls')),
     url(r'^admin/', include(admin.site.urls)),
 )