[WIP] [Validator] Allow to set "validatedBy" as option

This change makes the constraints more flexible by allowing to set the class (that validates the constraints) as option

Why? If i want to reuse an existing constraint e.g. Date but with my own validator i have to create a new class that extends the Date constraint class - just to override the "validatedBy" method!

With this change:
new Date(array('validatedBy' => "Yet\Another\DateValidator"));

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

todo if this pr will be accepted:

- [ ] submit changes to the documentation