Fix #678 -- Data shredders for personally identifiable information (#817)

* Add data shredders for PII

* First working shredder

* Add more shredders

* Add new shredders and download confirmation

* tmp

* PayPal, Stripe, banktransfer

* Add icon to logs

* Untested payment log shredders

* Add waiting list shredder

* First tests

* Add tests for shredders

* Improve templats, link to shredder

* Test payment info shredders

* More tests

* Documentation

* Fix enabled flag in payment provider overview

* Fix minor issues

doc/development/api/quality.rst

@@ -0,0 +1,125 @@
+.. highlight:: python
+   :linenothreshold: 5
+
+.. _`pluginquality`:
+
+Plugin quality checklist
+========================
+
+If you want to write a high-quality pretix plugin, this is a list of things you should check before
+you publish it. This is also a list of things that we check, if we consider installing an externally
+developed plugin on our hosted infrastructure.
+
+A. Meta
+-------
+
+#. The plugin is clearly licensed under an appropriate license.
+
+#. The plugin has an unambiguous name, description, and author metadata.
+
+#. The plugin has a clear versioning scheme and the latest version of the plugin is kept compatible to the latest
+   stable version of pretix.
+
+#. The plugin is properly packaged using standard Python packaging tools.
+
+#. The plugin correctly declares its external dependencies.
+
+#. A contact address is provided in case of security issues.
+
+B. Isolation
+------------
+
+#. If any signal receivers use the `dispatch_uid`_ feature, the UIDs are prefixed by the plugin's name and do not
+   clash with other plugins.
+
+#. If any templates or static files are shipped, they are located in subdirectories with the name of the plugin and do
+   not clash with other plugins or core files.
+
+#. Any keys stored to the settings store are prefixed with the plugin's name and do not clash with other plugins or
+   core.
+
+#. Any keys stored to the user session are prefixed with the plugin's name and do not clash with other plugins or
+   core.
+
+#. Any registered URLs are unlikely to clash with other plugins or future core URLs.
+
+C. Security
+-----------
+
+#. All important actions are logged to the :ref:`shared log storage <logging>` and a signal receiver is registered to
+   provide a human-readable representation of the log entry.
+
+#. All views require appropriate permissions and use the ``event_urls`` mechanism if appropriate.
+   :ref:`Read more <customview>`
+
+#. Any session data for customers is stored in the cart session system if appropriate.
+
+#. If the plugin is a payment provider:
+
+  #. No credit card numbers may be stored within pretix.
+
+  #. A notification/webhook system is implemented to notify pretix of any refunds.
+
+  #. If such a webhook system is implemented, contents of incoming webhooks are either verified using a cryptographic
+     signature or are not being trusted and all data is fetched from an API instead.
+
+D. Privacy
+----------
+
+#. No personal data is stored that is not required for the plugin's functionality.
+
+#. For any personal data that is saved to the database, an appropriate :ref:`data shredder <shredder>` is provided
+   that offers the data for download and then removes it from the database (including log entries).
+
+E. Internationalization
+-----------------------
+
+#. All user-facing strings in templates, Python code, and templates are wrapped in `gettext calls`_.
+
+#. No languages, time zones, date formats, or time formats are hardcoded.
+
+#. Installing the plugin automatically compiles ``.po`` files to ``.mo`` files. This is fulfilled automatically if
+   you use the ``setup.py`` file form our plugin cookiecutter.
+
+F. Functionality
+----------------
+
+#. If the plugin adds any database models or relationships from the settings storage to database models, it registers
+   a receiver to the :py:attr:`pretix.base.signals.event_copy_data` or :py:attr:`pretix.base.signals.item_copy_data`
+   signals.
+
+#. If the plugin is a payment provider:
+
+    #. A webhook-like system is implemented if payment confirmations are not sent instantly.
+
+    #. Refunds are implemented, if possible.
+
+    #. In case of overpayment or external refunds, a "required action" is created to notify the event organizer.
+
+#. If the plugin adds steps to the checkout process, it has been tested in combination with the pretix widget.
+
+G. Code quality
+---------------
+
+#. `isort`_ and `flake8`_ are used to ensure consistent code styling.
+
+#. Unit tests are provided for important pieces of business logic.
+
+#. Functional tests are provided for important interface parts.
+
+#. Tests are provided to check that permission checks are working.
+
+#. Continuous Integration is set up to check that tests are passing and styling is consistent.
+
+H. Specific to pretix.eu
+------------------------
+
+#. pretix.eu integrates the data stored by this plugin with its data report features.
+
+#. pretix.eu integrates this plugin in its generated privacy statements, if necessary.
+
+
+.. _isort: https://www.google.de/search?q=isort&oq=isort&aqs=chrome..69i57j0j69i59j69i60l2j69i59.599j0j4&sourceid=chrome&ie=UTF-8
+.. _flake8: http://flake8.pycqa.org/en/latest/
+.. _gettext calls: https://docs.djangoproject.com/en/2.0/topics/i18n/translation/
+.. _dispatch_uid: https://docs.djangoproject.com/en/2.0/topics/signals/#django.dispatch.Signal.connect