Update to spec v5.1

[jrhea]

Description

Tasks related to spec upgrade v5.1:

• On Genesis Updates (Part of Spec PR optimizations #711): On Genesis Updates (Part of Spec PR #711) #545
• Use signed_root For Block ID Purposes in Blocks/State - (Spec PR Tidy up BLS reference tests #816): Use signed_root For Block ID Purposes in Blocks/State - (Spec PR #816) #518
• Employ consistent style for function naming: Employ consistent style for function naming  #500
• Minor formatting/typos/etc Minor formatting/typos/etc #494
• Update Eth2Genesis Event - (Deposit_Contract PR Support UInt types in Java #22): Update Eth2Genesis Event - (Deposit_Contract PR #22) #493
• Update Eth2 Deposit Event - (Deposit_Contract PR Research on Pantheon, Web3j, Cava libraries for data types #21): Update Eth2 Deposit Event - (Deposit_Contract PR #21) #492
• Minor refactor to process_slashings to reduce repeated computation (Spec PR Fixes circular dependency that prevents a unified Deposit class #714): Minor refactor to process_slashings to reduce repeated computation (Spec PR #714) #490
• Make 'Any active validator' statements stricter (Spec PR Log epoch events #703): Make 'Any active validator' statements stricter (Spec PR #703) #489
• Do not check withdrawal credentials for existing validators (Spec PR Update Reference Tests (v0.7.1) #750): Do not check withdrawal credentials for existing validators (Spec PR #750) #487
• Cache justified/finalized roots in state for use in state transition (Spec PR Correctly Implement New SOS/SSZ Functionality #756): Cache justified/finalized roots in state for use in state transition (Spec PR #756) #483
• Only attempt to reward proposer if attestation exists for validator index (Spec PR Fix QuartzTimer issue #744): Only attempt to reward proposer if attestation exists for validator index (Spec PR #744) #481
• Handle get_base_reward when no previous balance (Spec PR Order Validators in Shuffling Test by Index #718): Handle get_base_reward when no previous balance (Spec PR #718) #480
• Handle when no attestations available for crosslinking (Spec PR BLS verify bug #717): Handle when no attestations available for crosslinking (Spec PR #717) #479
• Fix committee assignment bugs (Spec PR making profiling simpler #699): Fix committee assignment bugs (Spec PR #699) #478
• Fix latest_randao_mixes initialization value (Spec PR Make sure to gossip from outside peer communications #713): Fix latest_randao_mixes initialization value (Spec PR #713) #477
• Add HistoricalBatch tuple, remove merkle_root in favor of hash_tree_root functions. - (Spec PR Make this thing work #739): Add HistoricalBatch tuple, remove merkle_root in favor of hash_tree_root functions. - (Spec PR #739) #476
• Fix the "ready to exit" condition in update_validator_registry (Spec PR Implement beaconchain_peers metric #705): Fix the "ready to exit" condition in update_validator_registry (Spec PR #705) #475
• Fix up previous epoch logic around genesis (Spec PR Remove extra comment at the top of the file #672): Fix up previous epoch logic around genesis (Spec PR #672) #474
• Epoch Transition at Start of Epoch - (Spec PR Update README.md #732, Check that G1 and G2 points lie in the correct subgroups when created #741): Epoch Transition at Start of Epoch - (Spec PR #732, #741) #473
• Favor Higher Hash Tree Root for Ties in LMD GHOST - (Spec PR Gossip swap #737): Favor Higher Hash Tree Root for Ties in LMD GHOST - (Spec PR #737) #472
• Clarify basic/non-basic SSZ types - (Spec PR v0.7.1 Fork Choice Updates #724): Clarify basic/non-basic SSZ types - (Spec PR #724) #471
• Add tuple lengths to eliminate length mixin for some BeaconState, Deposit fields - (Spec PR v0.7.1 Honest Validator Updates #723): Add tuple lengths to eliminate length mixin for some BeaconState, Deposit fields - (Spec PR #723) #470
• SSZ Spec Changes - (Spec PR adding additional filters to flow and caching of committees #696): SSZ Spec Changes - (Spec PR #696) #469
• Remove signature/proof_of_possession from message_hash calculation. - (Spec PR Constants update (v0.7.1) #725): Remove signature/proof_of_possession from message_hash calculation. - (Spec PR #725) #468
• Bugfixes (in progress by @cemozerr, @schroedingerscode, @akhila-raju)
• Merge to master (will be started after bugfixes completed)

[akhila-raju]

Did a run-through of all of the checked tasks and implemented those that were missing. The tasks that still need to be looked at are mostly the ones related to SSZ and Eth2Genesis/Deposit events.

[akhila-raju]

Did one more pass-through; all that's missing is 3 SSZ-related tasks that @schroedingerscode will look over, 2 deposit contract tasks I will work on, bug fixes which @cemozerr, @schroedingerscode, and I are working on, and then we have merge to master!

[jrhea]

resolved by #687