* introduce candidatedescriptor type
* add PoVDistribution message type
* loosen bound on PoV Distribution to account for equivocations
* re-export some types from the messages module
* begin PoV Distribution subsystem
* remove redundant index from PoV distribution
* define state machine for pov distribution
* handle overseer signals
* set up control flow
* remove `ValidatorStatement` section
* implement PoV fetching
* implement distribution logic
* add missing `
* implement some network bridge event handlers
* stub for message processing, handle our view change
* control flow for handling messages
* handle `awaiting` message
* handle any incoming PoVs and redistribute
* actually provide a subsystem implementation
* remove set-builder notation
* begin testing PoV distribution
* test that we send awaiting messages only to peers with same view
* ensure we distribute awaited PoVs to peers on view changes
* test that peers can complete fetch and are rewarded
* test some reporting logic
* ensure peer is reported for flooding
* test punishing peers diverging from awaited protocol
* test that we eagerly complete peers' awaited PoVs based on what we receive
* test that we prune the awaited set after receiving
* expand pov-distribution in guide to match a change I made
* remove unneeded import
Robert Habermeier