More granular rewards

[djrtwo]

Issue

We currently only reward attestations for two things

• voting on the correct casper target
• voting on the correct shard_block_hash

This ends up not granularly incentivizes two other components of the voting process:

• voting on the correct casper source
• voting on the correct beacon_block_hash for your assigned slot

Proposed solution

• Give 1/4 of the total reward for individually satisfying each of the 4 above criteria
• multiply the sum of the 4 rewards above by the adjust_for_inclusion_distance to adjust for late inclusion
• An AttestationRecord can only be included in the block if voted on the correct source so the baseline reward for validators that got an attestation included is 1/4 of the total reward.
• rework BASE_REWARD_QUOTIENT and reward_quotient such that 1/reward_quotient is actually the max amount by which your deposit can grow per cycle. (rather than right now, it is 2/reward_quotient) That means that each of these items should be rewarded a max 1/(4 * reward_quotient)

[vbuterin]

Agree!

Though I would also say multiply the sum of the 4 rewards above by the function which reduces your reward if the vote took longer than the minimum to include.

[djrtwo]

waiting for #217 to reduce merge conflicts

[djrtwo]

closed via #290