Added query clauses to 'exists' validator

Added possibility to parse query clauses to 'exists' validator.

Eg:

$validator = $this->validator->create($this->request->post(),
[
   "user_id"     => "required|exists:users,id,activated,=,1,banned,=,0",
   "customer_id" => "required|exists:customers,id,type,=,reseller,activated,=,1"
]);


Parse unlimited parameters following the the sequence: 'operator','column','value'