request should be able to 'seed' requestScoped objects

[jknack]

This issue is related to #32. From request object it should be possible to seed a RequestScoped object:

user("*", req -> {
  req.set(Type.class, new Type());
}

seed method(s) looks like:

  Request set(final Class<?> type, final Object value);

  Request set(final TypeLiteral<?> type, final Object value);

  Request set(Key<?> key, Object value);