implement adding options to hosting packages

- fix unique constraints on CustomerDiskSpaceOption and
  CustomerUserDatabaseOption to allow multiple options from the same template
  for hosting packages
- fix disk space calculation in CustomerHostingPackage
- implement hostingpackages forms AddDiskspaceOptionForm, AddMailboxOptionForm,
  AddUserDatabaseOptionForm
- implement hostingpackages.views.AddHostingOption
- add new URL pattern add_hosting_option to hostingpackages.urls
- add template hostingpackages/add_hosting_option.html
- link items on hostingpackages/customerhostingpackage_option_choices.html to
  add_hosting_option

gnuviechadmin/hostingpackages/migrations/0005_auto_20150125_1508.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('hostingpackages', '0004_customerhostingpackagedomain'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='diskspaceoption',
+            options={},
+        ),
+        migrations.AlterUniqueTogether(
+            name='customerdiskspaceoption',
+            unique_together=set([]),
+        ),
+    ]

gnuviechadmin/hostingpackages/migrations/0006_auto_20150125_1510.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('hostingpackages', '0005_auto_20150125_1508'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='userdatabaseoption',
+            options={},
+        ),
+        migrations.AlterUniqueTogether(
+            name='customeruserdatabaseoption',
+            unique_together=set([]),
+        ),
+    ]