Bump Peerbit version for performance upgrades and sync fixes, and remove retrocompatibility mode

This bumps peerbit to 4.1.2 and @peerbit/document to 8.0.6 in order to hopefully make both syncing and querying (and thus page generation) faster, and fix some of the syncing issues. However backwards compatibility is broken so it requires a manual upgrade, but the difficulties associated with this should hopefully be ameliorated with the recent backup utility page at backup.html introduced in 4cda224a. Peerchan is bumped from 0.0.2 to 0.0.3 due to this compatibility break.