Add car manufacturer

User Story:
As a car salesperson
I want to record a car manufactuer
So that I can keep track of the types of cars found in the lot

Acceptance Criteria:
I must specify a manufacturer name, and country.
If I do not specify the required information, I am presented with errors.
If I specify the required information, the manufacturer is recorded and I am redirected to enter another new manufacturer.

*******************

User Story:
As a car salesman
I want to record a car listing's manufacturer
So that I can keep track of its manufacturer

Acceptance Criteria:
When recording a car listing, I want to optionally associate it with its manufacturer.
If I delete a manufacturer, the manufacturer and its primary key should no longer be associated with any car listings.