Binder could create instances even for classes without public default constructor

[asolntsev]

Sometimes we want to bind a class with play Binder, but leave its default constructor private or package-private, so that "normal" application code could not use it.

Like this:

public class Person {
  private Person() {
    // this should be used by Play Binder
  }

  public Person(String firstName, String lastName) {
    // this should be used by application code
  }
}

[asolntsev]

done in branch 1.4.x