[Web of Trust] Ranking system for peers

Define how peers are ranked for trust.

The manifesto describes the trust concept as:

Trust is ranked for each peer
- How much you trust what they're adding
- How much you trust what they're deleting
- How much you trust what they're tagging/annotating

Trust is transitive, e.g.:
- There are three peers, A B C, with A connected to B, B connected to C
- Peer A trusts peer B 50%
- Peer B trusts peer C 75%
- Because of the transitive trust, this means that A trusts C 37.5% (50% of 75%)