Refactor to add PeerId entity

[elct9620]

• Remove helper.go
• Add PeerId value object

This design is to support lookup Peer by device public key and peer public key

// in memory peer store
var peers map[PeerId]*Peer = make(map[PeerId]*Peer, 0)

// Lookup by PeerId
p1 := entity.NewPeerId([]byte{0}, []byte{1})
p2 := entity.NewPeerId([]byte{0}, []byte{1})

fmt.Printf("Is same: %t\n", peers[p1] == peers[p2])
// => Is same: true