Align to spec v0.11

[terencechain]

With the release of v0.11 to facilitate new shading proposal. This PR tracks to the progress to align Prysm to v.0.11 which is important for multi client test net. The experimental branch for this is:

The v.0.9 consists of the following:
https://github.com/prysmaticlabs/prysm/tree/spec-v0.11

Beacon chain

• Adjust hysteresis to avoid initial over-deposit incentive (adjust hysteresis to avoid initial over-deposit incentive ethereum/consensus-specs#1627)
• Add proposer_index to BeaconBlock (add proposer index to BeaconBlock ethereum/consensus-specs#1626)
• Handle rewards overflow (handle rewards overflow  ethereum/consensus-specs#1635)
• Add genesis_validators_root to BeaconState to support better fork separation (add eth2 key/value ENR to phase 0 p2p ethereum/consensus-specs#1614, Gossip topics with fork digest ethereum/consensus-specs#1652)
• Denominate Eth1 voting period in epochs (Eth1 voting period in epochs [updated for configs/phase1/tests compat.] ethereum/consensus-specs#1649)
• Attestation must match target to match head for rewards (Must match target to match head ethereum/consensus-specs#1653)

Fork choice

• Pull out some helper functions for better code reuse across forks [No Substantive Change] (Phase 1 rebase ethereum/consensus-specs#1504)

Validator

• BeaconBlock slashing is per-slot (reflect this in v-guide) ([validator guide] beacon block is per-slot slashing ethereum/consensus-specs#1612)

Networking

• Add libp2p-noise specification (Add libp2p-noise specification ethereum/consensus-specs#1607)
• Remove head_block_root from BeaconBlocksByRange (drop head_block_root from BeaconBlocksByRange ethereum/consensus-specs#1604)
• Add subnet validations for DoS resistance (Add subnet validations for DoS resistance ethereum/consensus-specs#1615) Add DoS resistance for v0.11 #5158
• Add lower bound slot condition on block gossip (add lower bound slot condition on block gossip ethereum/consensus-specs#1616) Align finalized slot check with v0.11 #5166
• Add DoS prevention validation conditions to additional gossipsub topics (add DoS prevention validation conditions to additional gossipsub topics ethereum/consensus-specs#1617)
• Use snappy frames to support streaming (RPC chunks with streaming SSZ decoding, snappy frames, and stricter DOS limits where possible. ethereum/consensus-specs#1606)
• Add eth2 key/value to ENR (add eth2 key/value ENR to phase 0 p2p ethereum/consensus-specs#1614)
• Add fork digest to gossipsub topics for simple fork versioning of messages and to Status message (Gossip topics with fork digest ethereum/consensus-specs#1652)