If a module installs additional dependencies, they should show up as installed right away

EDIT: Never mind, this idea won't work.

#3 gives me an idea: we could add a new AJAX command that forces all visible instances of Project Browser to reload their data, using the previously known set of query parameters.

Activators which know that dependencies were enabled -- and we could add a trait for activators to easily figure this out -- could return this command, and that would get everything that was installed, to show up as installed.

It's a bit brute force, but I'm not sure there's a cleaner way to do this. I've been puzzling over this one for days and the current (solid) architecture just doesn't allow it to be done using RefreshProjectsCommand, at least not without some very complicated contortions.

Assigning to myself to see if this can work at all.

Discussed this with @chrisfromredfin in Slack and what we decided is that the smartest way to do this is for the frontend to explicitly request a refresh of all visible projects, since it (and only it) knows what projects are visible to the user.

Basically what I proposed in #3. I'm okay with it.

The PHP and JavaScript side of this wasn't hard, but this will need an explicit test.

Writing a test was surprisingly quick!