Lua scripts: "active" status should interact better with registered functions

[RetroEdit]

The basic idea is:

• A script that has registered functions should still be marked as "active" with the green checkmark
  • Perhaps a script where the last registered function is later unregistered should change to inactive?
• Toggling the script to inactive unregisters any callbacks that the script registered

This is only a design proposal, but it would make the interface more consistent and the behavior clearer in my opinion.

It would also solve the issue where unloading/reloading a script creates more and more registered functions; this is not a large issue though, because Script > Registered Functions... can be used to remove registered functions.

Related: #4499

[vadosnaprimer]

Agreed!