Fixes: #158

Final port to Python 3 only.

See merge request !75

Bump minor version for the next release.

See merge request !76

Fix pep8 errors.

Add a pending migration

See merge request !77

Django-2.0 and Python 3 compatibility

See merge request !79

unspecified encoding.

Handle attachments returned from Scrubber as bytes or strings with

Closes #171

See merge request !85

Provide a pagination class so pagination is actually enabled

See merge request !78

Update demo server and Python support metadata.

See merge request !87

This reverts commit c703f2ff.

Remove obsolete minifier dependencies

See merge request !84

Replace 'load staticfiles' with 'load static'  as required in new versions of Django

See merge request !90

Remove robots.txt from urls.py

Closes #176

See merge request !91

See the doc update for details.

Add the possibility to store attachments on the filesystem

See merge request !92

Case seen in the wild:
```
ERROR 2018-06-09 23:09:37,454 22197 django.request Internal Server Error: /archives/api/mailman/archive
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python2.7/site-packages/hyperkitty/views/mailman.py", line 68, in _decorator
    return func(request, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/hyperkitty/views/mailman.py", line 114, in archive
    add_to_list(mlist_fqdn, msg)
  File "/usr/lib/python2.7/site-packages/hyperkitty/lib/incoming.py", line 149, in add_to_list
    email.save()
  File "/usr/lib/python2.7/site-packages/django/db/models/base.py", line 734, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/lib/python2.7/site-packages/django/db/models/base.py", line 762, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/usr/lib/python2.7/site-packages/django/db/models/base.py", line 846, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/usr/lib/python2.7/site-packages/django/db/models/base.py", line 885, in _do_insert
    using=using, raw=raw)
  File "/usr/lib/python2.7/site-packages/django/db/models/manager.py", line 127, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/django/db/models/query.py", line 920, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 974, in execute_sql
    cursor.execute(sql, params)
  File "/usr/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/lib/python2.7/site-packages/django/db/utils.py", line 98, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
DataError: invalid byte sequence for encoding "UTF8": 0xed 0xb5 0xb5
```

Add missing Message-IDs in hyperkitty_import.

Closes #180

See merge request !94

Remove old cache implementation from django_mailman3.

See merge request !95

Do not use Django-Q at all when running in sync mode.

See merge request !98

Do not filter out emails with thread_order None.

Closes #151

See merge request !97

Document and tasks module and add callback hook for tasks.

See merge request !96

Implement update index for one list.

Closes #175

See merge request !99

Running hyperkitty_warm_up_cache no longer depends on verbosity.
Message about updating search index is revised.

hyperkitty_import minor fix and message update.

See merge request !100