Add NiceHash extranonce patch

All commit from ( https://github.com/nicehash/sgminer/commits/master ):
- handle mining.set_extranonce method
- subscribe for mining.extranonce
- Allow disable extranonce subscribe
- Send subscribe request before auth
- Change mining.set_extranonce method as stratum notification
- Set extranonce.subscribe timeout to 2sec
- Protect pool name with lock
- Some tweaks for extranonce
- Handle pool response, who send errors in invalid format
- Move no-extranonce-subscribe parameter to a pool config
- Fix nonce1 and sessionid memory leak