Merge pull request #1 from rusinekm/michal

modele zrobione
Merge pull request #2 from rusinekm/michal

Michal
First test for Car model
test for blank in Car + helper method
validation for brand presence
Test for blak properties + validations
Tests and validations for integer in mileage, production_year
Merge pull request #4 from rusinekm/adam

Adam
dodany index car oraz sprawdzanie czy samochod jest wypozyczony oraz do kogo.