TW-17: UI improvements

- better backround & colors
- redirect on registration
TW-17: Cleans up the navbar
TW-17: Adds a favicon
TW-17: Adds a default image for mates
TW-17: Uses the byte array stored in DB for images
TW-17: Gray out OFFLINE images
TW-17: Improves how images are stored

* Stores the file content in the db
* Uses it as a byte array to serve the image
TW-17: Fixes tests and linters
Merge branch 'feature/TW-17_UI' into develop