Add a very simple synchronous notification dispatcher

[tamuri]

For #1753. Adds a global dispatcher of notifications for listeners that can be used in the core framework and by model modules. I avoided using the more typical naming event or signal because they are already used.

[marghe-molaro]

Applied this in PR #1753, and seems to be working well!

Note that I am currently including any checks on whether dispatch of notification is really necessary at the listener's end, rather than before the dispatch takes place; this makes things tidier but may impact performance if a lot of notifications were not necessary?

[tamuri]

Note that I am currently including any checks on whether dispatch of notification is really necessary at the listener's end, rather than before the dispatch takes place; this makes things tidier but may impact performance if a lot of notifications were not necessary?

Can you point me to an example?

[marghe-molaro]

Just noting that test_save_load_pickle_after_simulating in test_simulation.py fails when invoking dispatches, presumably because of how dill.dump handles them?

[tamuri]

Thanks - I've pushed a change in this PR that fixes that problem.