Model CRUD API

[VasAtanasov]

• As a Vehicle API user, I want to be able to retrieve a list of all vehicle maker's models. #48
• As a Vehicle API user, I would like to have the ability to add a maker's model. #49
• As a Vehicle API user, I would like to have the ability to edit a maker's model. #50
• As a Vehicle API user, I would like to have the ability to delete a maker's model. #51