Turn magic number/orphan values into literals

Take remaining magic numbers floating in modules (more common in settings) and convert them into literals using standard Mayan variable nomenclature. Place the new literals into literals.py modules. Turning these numbers into literals provide contextual information.

Example: Default setting values in the documents app. https://gitlab.com/mayan-edms/mayan-edms/-/blob/master/mayan/apps/documents/settings.py#L178