Refactor Logic around DataFromPeer

[ceilican]

Right now the message DataFromPeer is received by two actors: PeerSynchronizer and NodeViewSynchronizer. And it is sent by NetworkController, which has a sophisticated and generic message handling mechanism to decide if it should send a DataFromPeer message to PeerSynchronizer or to NodeViewSynchronizer.

The question is: do we need all this generality? I think it is compromising clarity and making the code that handles these messages in PeerSynchronizer and NodeViewSynchronixer more complex than it needs to be. Maybe there is a simpler to accomplish the same thing, although I don't have a clear idea how at the moment.

Maybe a first step could be to specialize DataFromPeer into more specific message classes, such as ModifiersFromPeer, InvDataFromPeer, SyncInfoFromPeer, PeersFromPeer, and so on...