* move gossip/NCP off assuming anything about its address
* use a single socket to send and receive gossip
* remove --addr/-a from CLIs
* rearrange networking utility code
* use Arc<UdpSocket> to share the Sync-safe UdpSocket among threads
* rename TestNode to Node
TODO:
* re-enable 127.0.0.1 as a valid address in crdt
* change repair request/response to a similar, single socket
* pick cloned sockets or Arc<UdpSocket> for all these (rpu uses tryclone())
* update contact_info with network truthiness instead of what the node
says?
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