remove network pause

Add optional parameter to Worker constructor for sleep period.
fix client repeat-disconnect loop.
removed resolver from getifaddr dance (not reqd) and updated getifaddr code (needs windowz/linux testing).
don't accept new connections if listenport bind fails (possible due to OS firewall settings).
only use upnp w/ipv4 addresses.
re: disconnect loop. Looks like ethhost session isn't deallocating once stopped. Thinking UI might have shared_ptr. For now, letting dealloc/quit continue as long as isOpen returns false -- maybe okay since network will be halted. Also, it maybe possible the issue is due to network thread not running after disconnect so packets aren't tx/rx to kill peer -- either way, it's possible remote end doesn't ack disconnect and timeout/force-close-dealloc is required, so will need more attention later.
Why not call it "externalPort"?