Miners are now get rewards

[tbrand]

Currently miners will not get any rewards even if it find a correct nonce.
This update allows miners to get rewards according to it's hash rate.

1. Miners will get 3/4 of total served amounts of coinbase, remaining amounts(1/4) will serve to the hosting node.
2. The ratio of the rewards depends on it's hash rate.
   1. The hash rate is calculated from the # of the nonces sent by miners
   2. Since the difficulty of the miner's PoW is easy comparing to the real difficulty, multiple nonces are sent from miners. (It's the same idea of well known Mining Pool)

For example, let's assume that

• Total served amount from coinbase is 10.0.
• Miner A found 8 nonces
• Miner B found 4 nonces

Then,

• Miner A will get 5.0 coins: (10.0 * 3/4) * (8/12)
• Miner B will get 2.5 coins: (10.0 * 3/4) * (4/12)
• Node will get 2.5 coins: 10.0 - 5.0 - 2.5

This commit also includes many bug fixes.