Option to run Discovery V4 and V5 on the same port

[alexb5dh]

• Versions to use (v4, v5, both) are now configurable, but same port is used when multiple are enabled. In such case same UDP connection (Netty IDatagramChannel) is used.
• Channel is injected into Lantern.Discv5 implementation via adapter for its IUdpConnection.
• Connection-management code moved from DiscoveryApp to a new DiscoveryConnectionsPool.
• Discovery initialization code moved from InitializeNetwork to a new CompositeDiscoveryApp.
• When both versions are enabled, all incoming messages are received by v4 handler first, which than forwards it to v5 if it doesn't manage to recognize the format. Otherwise, only enabled handler is being used.

Depends on Pier-Two/Lantern.Discv5#105 being published on Nuget