Bugfix: Editing of instructions

The instructions were not properly shown after canceling or submiting
the editing form.
pep8 checker: Profiles app is now gone
missing parameter for Apache proxying

To be able to use Apache proxying, one needs to add a ProxyPreserveHost parameter. One also need to adjust the Pootle configuration file.
Drop django-maintenancemode

We have decided against it as it has not been updated in a while.
Users who wish to use maintenancemode can easily install and add it
in their settings.