A user can attach files to a task

[fynnfeldpausch]

As a user, I want to attach files to a task so that I can store additional information.

Acceptance criteria

• the user can upload a file
• the file is attached to the task
• the file can be downloaded

Optional acceptance criteria

• the user can see previews for images

Additional information
We prefer quality over quantity. Clean code is a given. We expect all test to run.