adapt cmd/cli to new backend

- new flag nat for nat support UPNP|PMP
- new flag pmp for PMP gateway IP
- add NatType to utils/cmd to get p2p.NAT from nat type string
- obsolete usepnp flag
- get rid of IsUpToDate and sleep in miner start
- ethereum constructor takes nat type, port, maxpeer
- add pubkey arg to client identity