Get all the open modal instances using the NgbModal

[ahadjithoma]

Feature Request:

It would be nice if using the NgbModal we could get the instances of all the opened modals.
Since the service has the hasOpenModals method, i expect that getting the instances of them won't be an difficult.

What we are trying to do:

Some modal components are extending a class for additional checks whether they can be closed or not. In our app.component we are subscribing to route events and we close all modals by calling the dismissAll method but we would like to check whether those modals can be closed or not before closing them. This can be done by calling a method inside the modal component. With that said, we need the instances of all the currently opened modals.

Thanks