Remove unused nTargetNewSpacingWorkMax.
Rename/Update and Implement nNewTargetTimeSpan to 120 blocks. 14400 / 120 = 120
Clean up unneeded garbage in GetNextTargetRequired. There were no PoS blocks created < 100.
Update GetNextTargetRequired to better handle negative nActualSpacing values. (block timestamp
is older than it's parent)