Create rewards table to track miner, uncle and genesis rewards

[ankitchiplunkar]

Is your feature request related to a problem? Please describe.
If we run ether_sql in parallel, then creating the current_state and current_storage (#25) would not be possible because these tables are derived one block after the another. This creates a chicken and egg problem when ether_sql runs in parallel since to solve the issue: #24 we need the current_stateand current_storage tables but to get those tables we need past rewards in the state_diff.

Describe the solution you'd like
Proposed rewards schems:

REWARDS = ['block_number',
                   'reward_wei',
                   'fees_wei',
                   'to',
                   'timestamp',
                   'reward_hash',
                   'reward_type']

[ankitchiplunkar]

Similar to issue: #24