Distinguish counts of crawled pages between successes and errors

[boogheta]

Currently a crawl status counts a total of pages which includes errors.
So when a webentity does not exist on the web for instance, its crawl will still say 1 crawled page (or even N if given multiple startpages) although it's a 404 or 500.
It would make more sense for the users to see the number of well crawled pages (and maybe also display a number of error pages)