* Convert BlockGHOSTDAGData from an interface to a public struct with getters
* Move hashes.Less to externalapi so it can access the hashes directly without copying
* Reduce calls to ghostdagstore.Get in blueWindow
* Simplify the logic in RequiredDifficulty and reuse big.Int
* Remove bigintpool as its no longer used
* Use ChooseSelectedParent in RequiredDifficulty instead of looping over the parents
* Remove comment
* Replace blueScore with blueWork in ghostDAG SelectedParent selection
* Add blueWork to protopuf ghostdag data
* Auto generate protobuf go code
* Serialize/Deserialize blueWork when converting to protobuf
* pass block header store to ghostdagmanager
* Convert tal's ghostdag2 implementation to blueWork
* Change finality test to check the blueWork instead of blueScore
* Update ghostdag_test to pass blockHeaderStore to ghostdag, and test all networks genesis headers
* Add sanity blueWork check to ghostdag_test
