Network protocol update

[catena2w]

Changes:

• Add version field to all p2p messages
• Do not send messages which which version is higher then peer version
• Refactoring: extract common PeerData structure from PeerInfo and Handshake
• Refactoring: HandshakeSerializer => HandshakeSpec
• Refactoring: make InvData and ModifiersData a case class instead of a tuple
• Distribute PeerData in Peers message
• Only send recently seen and connected peers on GetPeers request
• Remove not responding peers from local peers database (Close #301)
• Remove peer from local database on handshake parsing failure

[coveralls]

Coverage remained the same at 46.513% when pulling 38e14c79e1bb872d3cb3e36459c1414c5cf48c2a on p2pversion into d1198271f8f061577042136d7442ab1fa4f19efe on master.