Add checkpoints for staking pool

1.Add checkpoints for staking pool.
2.Remove deprecated APIs.

Fixed staking pool reward

This is a hard fork. The new consensus will active at 658700 block.

Fixed withdraw staking pending reward

1.Fixed withdraw staking pending reward;
2.Set network protocol minimal version;
3.Add Remove transaction to GUI.

Fixed max difficulty limit

1. Fixed max difficulty limit. It's a hard fork, and will active at 654601;
2. Remove old coins locked check.

Use available website

1. Use available website
2. Fixed staking pool status scanning

Update QtWallet to support DPOS

v2.1.1

update to v2.1.1

v2.1.0

init dpos