Strict Checkpoints

Gridcoin Research 3.1.7.6/7.0:
Mandatory Upgrade

- Adjusted fork diff threshhold to .01
- Adjusted netsoft tolerance percent to 1.3
- Made it slightly easier to mine @ < .01 diff (network bootstrap)
- Added IsUserQualifiedToSendCheckpoints - requiring a Mag consensus
accuracy of 20+ to broadcast a checkpoint