Editable settings refactor - this change is to clear up confusion around editable settings being defined in a project's settings module. Previously when this happened, the settings.py module value would only serve as a default, which would be superceded by the db editable value as soon as the settings admin form is first saved. To address this, this change means that editable settings defined in the project's settings.py module now mark the setting as not editable, so it will always be the value used. We also include some handling for the migration case so that even with this change, editable settings already in the db that have a settings.py value defined will still use the db value and provide a warning.