ModuleNotFoundError: No module named 'paintstore'

Since after Jan 20th, 2019 if you use rolling releases and customize INSTALLED_APPS in your settings_local.py, it is possible that you'd see an error traceback like below:

Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 357, in execute
    django.setup()
  File "/usr/lib/python3.6/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/usr/lib/python3.6/site-packages/django/apps/registry.py", line 89, in populate
    app_config = AppConfig.create(entry)
  File "/usr/lib/python3.6/site-packages/django/apps/config.py", line 90, in create
    module = import_module(entry)
  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'paintstore'

This is because on Jan 20th, Hyperkitty removed dependency on paintstore and hence the settings needs to be updated for that.

SOLUTION: Remove paintstore from your INSTALLED_APPS.