[REF] 8.0 mgmtsystem nonconformity

Removed base_status dependency and reimplemented some of the methods that were missing to keep the `cases` working. 
Good catch on the constraint.

I haven't done this, but I think to clone a class you can do this:

```
class mgmtsystem_nonconformity_origin(models.Model):
    _name = "mgmtsystem.nonconformity.origin"
    _inherit = "mgmtsystem.nonconformity.cause"
```