NEW: Added ImportSchema support.

An Import Schema is a collection of Import Rules applied to a set of matching URLs.
Import schemas make it easier to tailor import rules for a diverse site, rather
than relying solely on ImportRule failover.
BUG http/https switching results in an exception
BUG Output the correct url when hitting a > 399 url
NEW: Limit the number of urls to crawl
NEW: Add the possibility to exclude URLs from being scraped
NEW Use the pagetype from the schema when importing