Module 5: Streams 2 is stringly typed

[xgillard]

This issue relates to #35 (actually this should be a subtask of the previous).

Streams 2 is "stringly typed" this is not how we should teach students to code.
The easiest and cleanest way to solve all questions si to define the following method:

private final static Predicate<Student> pred(final Map<String, Predicate<?>> conditions) {
    return (s) -> {
      for (Map.Entry<String, Predicate<?>> e : conditions.entrySet()) {
        switch (e.getKey()) {
          case "firstName":
            if (!((Predicate<String>) e.getValue()).test(s.getFirstName()))
              return false;
            else break;
          case "lastName":
            if (!((Predicate<String>) e.getValue()).test(s.getLastName()))
              return false;
            else break;
          case "section":
            if (!((Predicate<Integer>) e.getValue()).test(s.getSection()))
              return false;
            else break;
          case "courses_results":
            if (!((Predicate<Map<String, Double>>) e.getValue()).test(s.getCourses_results()))
              return false;
            else break;
          default:
            throw new RuntimeException("Unexpected key");
        }
      }

      return true;
    };
  }

One should rely on the type system to help student get a grasp on what should be done. Also, it would be great if we could show students how to combine predicates (and, or, not, ...)