Fix: Projects can be deleted with resources

[peaklabs-dev]

Note

-> I could have fixed this with a one line change by checking resource_count() > 0 before deleting the project, but I decided to refactor the code a bit to use isEmpty() as we use that in other places as well.

Changes

• Fix: Project with resources (compose base, services...) can be deleted, but the resources would of course still be there after the project was deleted (before deleting a project, we only checked applications, which is not enough).
• Improvement: Show better error message when deleting projects and environments.

Issues

• fix #3747