BlockMessage was broken because the repository 'connection' associated with the message's Block object was closed between message queuing and message sending.
The fix was to serialize Message subclasses on construction, thus freeing reliance on objects passed into constructor.
The serialized byte[] is held by the message between queuing and sending.
This forces messages into one of two 'modes': outgoing or incoming.
Outgoing messages contain serialized byte[] whereas incoming messages unpack a ByteBuffer into Message subclass fields.
As a result, all network message types have been refactored in this way.
More details in Message's class comment.
A knock-on effect is that incoming messages cannot then be sent out - a new message needs to be constructed.
Some changes needed to Arbitrary controller package classes in this respect.
Bonus: Network no longer needs broadcast threads because 'broadcasting' is now simply the act of queuing a message for many peers.
Instead of synchronizing/blocking in Peer.sendMessage(),
we queue messages in a concurrent blocking TransferQueue, with timeout.
In EPC, ChannelWriteTasks consume from TransferQueue, unblocking callers to Peer.sendMessage().
If a new message is to be sent, or socket output buffer is full,
then OP_WRITE is used to wait for socket to become writable again.
Only one ChannelWriteTask per peer can be active/pending at a time.
Each ChannelWriteTask tries to send as much as it can in one go.
Other minor tidy-ups.
As per work done by szisti in PR#45:
Extracted network 'Tasks' to their own classes.
Network.NetworkProcessor reduced to only producing Tasks.
Improved usage of SocketChannel interest-ops.
Eventually this might lead to reducing task-producing synchronization lock into more granular locks.
Work still needed to convert sending messages to a queue and to make use of OP_WRITE instead of sleeping to wait for socket buffer to empty.
Disabled PeerConnectTask producer from checking against connected peers via DNS as it's too slow.
Swapped Peer's replyQueues from SynchronizedMap(wrapped HashMap) to ConcurrentHashMap.
Other minor changes within networking.
