Issues with the exit dialog for an unsaved project

### Bug description

When exiting Audacity with an un-saved project the error message looks like a Musescore message as it talks about saving changes to the "score" which is basically un-Audacity.

Also note that you get this naggogram even if you exit from an empty (and thus clean) project (when there is really nothing to save).

It's also somewhat odd to be suggesting to a user that they might save a project in **Appdata > Local > ... >SessionData** which is really a system/app location, not really a sensible user storage location.

### Steps to reproduce

1. launch AU4 alpha
2. click the New Project
3. File > Exit
4. Observe: error message

### Expected behavior

A more appropriate error message

No naggogram when exiting a clean (empty) project

### Actual behavior

### Audacity Version

AU4 alpha

### Operating system

Windows

### Additional context

In contrast the exit naggogram in AU3 and earlier is better

Reproduce the issue in AU4 alpha on Windows by creating a New Project and choosing File > Exit. Compare the exit dialog with the AU3 example and verify behavior for both an unsaved project and an empty clean project. Done means the wording is appropriate for Audacity, clean projects do not prompt unnecessarily, and the suggested save location is sensible.

Written by the indexing model from the issue text.