Rework scraper interface

[rsubtil]

The scraper is working, but it's very simple and not yet robust:

• It's not possible to cancel a request
• Thread deadlocks if user quits scraping popup while querying information
• No way of retrying a scrape

[rsubtil]

Fixed by https://github.com/retrohub-org/retrohub/commit/dfd7dda967a5806d7df98030778a1c5d95e6cab8