Feature/improve parameter passing

This MR improves the passing of parameters to avoid unnecessary copying, especially with container objects.

It also allows passing nullptr to Promise::then() instead of QtPromise::noop. QtPromise::noop has therefore been deprecated.

Breaking Change:
The signature of Promise::all() and Promise::any() has been changed. Therefore, this is formally a breaking change. However, unless you explicitly rely on the exact signature of those methods, the change will not be breaking for you since the change is only from call-by-value to call-by-reference.