End the websocket download if a model changes state from online. Also
properly close both sockets and set isAlive to false, if the download is
closed or fails
This is the first version with working downloads for SD and HD. These
dowloads only work, if you are logged in. So at the moment you have to set the
session ID in the settings to make this work. The session ID can be copied
from a valid session in a browser.