Preload data when ?url= is present

[bartveneman]

We used to have this years ago, forgot why I removed it. Maybe it was because the triangle hoster was billing me big time for CPU time, dunno.

Considerations

1. When ?url= is present, scrape immediately, without user having to press 'analyze css'
2. Watch out for slow first contentful paint, maybe show a loading state first
3. Add heaps of tests, a lot of existing tests will have to be rewritten