Added custom HTTP header field for the login page to make it easier to recognize.
Added a Klient API.
Added a read API for Usluga.
Added a read API for Pojazd.
Added a read API for Wizyta.
Added a Zlecenie API.
Added a Zadanie API.
Hand-picked serialization fields for the API.
Added more constraints regarding null foreign keys.
Added uniqueness constraints to entities.