[PLAN] Improve server code

[raf555]

Plan to do after Mangadex release their v5. This plan is to improve server code such as reducing DRY code and more

• Make separated file for Mangadex API
• Make separated file for utility function
• Update Mangadex API to the latest version (after dex v5)
• Logging (esp. for error)
• Admin page/dashboard
• other (might update the issue later)

I am planning to do this after Mangadex v5 is released and may be finished around May perhaps.

[raf555]

• Make separated file for Mangadex API ----- done
• Make separated file for utility function ----- done

now waiting for mangadex v5