Change local.py to project_settings_local.py

[markfinger]

I found it confusing jumping onto a new project using ixc-django-docker as it is using different conventions for settings file names.

The project_settings_local pattern also helps to understand a project's current state as the file is sorted alphabetically with project_settings. Given that the root projects are filled with so much service/docker/CI cruft, collocation also helps with awareness that a local file exists.