Use modifiers for settings

[radiac]

Currently we have a way to extend INSTALLED_APPS, but looks for a better way to extend all list and dict settings - perhaps something like INSTALLED_APPS__APPEND?

[gabriels1234]

@radiac
Question: If I install pip install django-constance I could just send Django(INSTALLED_APPS=['constance'])? WOW!
Would you like a PR for INSTALLED_APPS__APPEND? This is already added with EXTRA_APPS (see:

nanodjango/nanodjango/settings.py

Line 30 in 9eb4755

INSTALLED_APPS = [

)