Added grabRepository function

[TavoNiievez]

$I->grabRepository significantly improves the readability of the tests that communicate with the database :)

as mentioned in the docblock, it works with:

• Entity objects,

$userRepository = $I->grabRepository($user);

• Entity classes,

$userRepository = $I->grabRepository(User::class);

• Repository classes,

$userRepository = $I->grabRepository(UserRepository::class);

• or even Custom Interfaces that have been implemented in a repository.

$userRepository = $I->grabRepository(UserRepositoryInterface::class);

It also includes validations in case of incorrect data and fails the test showing a corresponding error message.

@Naktibalda

[DavertMik]

Awesome!