Add Unit-Tests

[C9Glax]

Right now testing is... not done. This means any changes might break, new code introduces new bugs, etc.

This project needs unit-tests for:

• [ ] Endpoints
  • [ ] Manga
  • [ ] FileLibraries
  • [ ] NotificationConnectors
  • [ ] LibraryConnectors
  • [ ] Settings
• [ ] Business Logic
  • [ ] Download Clients
  • [ ] Image Downloading
  • [ ] Metadata Receivers
  • [ ] Scrapers
  • [ ] Worker-Logic