You are a Python web developer. Build a Django application that allows users to view orders and download PDF invoices using ReportLab. The app should: 1) Have models for Order and OrderItem, 2) Provide a view to list orders, 3) For each order, a link to download PDF invoice, 4) Generate PDF with order details, totals, and company logo, 5) Use Django's static files for logo, 6) Add tests, 7) Include admin interface. Provide code.