Add node discover function (#1032)

Add node discover function (#1032)

* Add node discover function

* Add dependent libraries

* Change discover nodeID to edd25519 pubkey

* Del unused secp256k1 lib

* Add discover debug info

* Del unused sha3 lib

* Del unused math function

* remove address book from switch level

* use discover to replace addrbook

* Chane discover rlp encode to go-wire encode

* Add test discover seed

* edit the log from info to debug

* edit the code

* remove pex call seed

* edit for fix bug

* edit the solonet config

* edit for debug

* make udp listen to config address

* handle error on start switch fail

* move discover outof switch

* handle the empty seed case

* edit the node select

* Ma's order

* remove a unused function