WIP: Restructure user discovery

bindings/ud.go

cmd/ud.go

ud/addFact.go

ud/comms.go

ud/confirmFact.go

ud/lookup.go

ud/manager.go

ud/register.go

ud/registered.go

ud/remove.go

ud/search.go

ud/store/facts.go

ud/store/facts_test.go

ud/store/store.go

ud/store/store_test.go

ud/store/ud/facts.go

ud/store/ud/facts_test.go

ud/store/ud/store.go

ud/store/ud/store_test.go