Issue/235/support makemmigration customisation

[rsmith013]

Harmonises the makemigrations and lintmigrations config loading code and sorts the priority order. As it was before, only Falsy default values could be overwritten by config options. I would also expect the command line to take priority over the config files.

This PR makes an opinionated preference for ordering of config sources where higher priority sources override lower priority settings. Open to discussion:

1. Command line
2. Django Settings
3. Config files
4. pyproject.toml

closes #235