* update Deposit and BeaconBlockHeader to 0.7.0
* update get_total_balance(...) and get_base_reward(...) to 0.7.0
* rename initial value constant BLS_WITHDRAWAL_PREFIX_BYTE to BLS_WITHDRAWAL_PREFIX
* mark minimal presets as entirely migrated to 0.7.0; update process_rewards_and_penalties(...) to 0.7.0
* specify that targeting 0.7.0; adopt 0.7.0 refactoring of bls_domain/get_domain to update get_domain(...) to 0.7.0; mark that mainnet constant presets and block header processing are 0.7.0-consistent; update process_justification_and_finalization to 0.7.0 to fix potential underflow errors
* address mratsim's comment to copy whole spec comment
e9180c490e