Implementing basic unwind process for Proof-of-stake (#3083)

* initial commmit

* gofmt

* flipped if statement

* flipped if statement (forgot to save)

* passing unwinding to status ch

* added unwinding constant

* took out unwinding

* added statusCh

* added a return statement and a second part to the if statement

* checking for parent hash

* checking for parent hash

* changed check to check for parentHash

* staged wrong file

* changed header check to parentHash check

* channged blockhash name to a better name

* changed it to check for header.Hash()

* changed name of blocknumber to blockHash

* changed bad block to common.Hash{}