Allow user specified django project

[mylibrar]

Is your feature request related to a problem? Please describe.
Right now the stave package contains a complete django project, including the settings.py, which is not very flexible and secure. We want to allow user to control the settings, hence it's better to package stave as a django app instead of a project.

Describe the solution you'd like
Remove settings.py in stave package and let user provide the configuration. We may also add an interactive interface in Stave CLI for user to set up the path of DJANGO_SETTINGS_MODULE.

Describe alternatives you've considered
If users choose not to provide DJANGO_SETTINGS_MODULE, stave should be able to automatically configure default settings for django.

Additional context
Add any other context or screenshots about the feature request here.