Load management statistics (low priority)

[toad]

More archaeology! Adds more load management info in advanced mode, efficiently/atomically. This allows testing theories such as "my peers are all bouncing around 50% load".

This touches (and slightly tidies up) load management but it should have no functional impact on it. In particular, RequestTracker.countAllRequestsByIncomingPeer is only used by the new UI code (and wasn't used at all by next).