Upgrade Heritrix

Currently we actually work with three different Heritrix upstreams

1. Internet Archive
2. Kristinn's in Iceland, containing his releases using various snapshots of 1) with his own modifications
3. Our own fork, based on 2) but with further modifications, including our upgrade of the bdb dependency to enable paging

There is no fundamental problem with this as long as the versions don't diverge too much, so we should try to pull as many changes as possible from 1) into 3). It would be especially interesting to see if https://github.com/internetarchive/heritrix3/pull/213 improves the general stability of H3.