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.
This and below are copy/paste of working code. I'd like to keep this code this way (defer refactoring) because upnp has problems. For example, it can be allocated but doesn't return true for isValid() and crashes if it's deallocated. unique_ptr implies a consistent alloc/dealloc model which upnp doesn't adhere to. Will add some docs.