Beacon chain light client support

[terencechain]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

This PR implements light client beacon chain support. It aligns with the following effort in eth2.0 repo:
ethereum/consensus-specs#2130

Implemented:

• Extend sync bits and signature fields to beacon block body, this is done in v1apha1, pushed to ethereumapi upstream
• Extend sync committee fields to beacon state, this is done in local proto
• Verify fastssz worked with above
• Add sync committee helpers
• Add process sync committee beacon block body logic
• Add update sync committee at epoch boundary logic
• Add Bitvector with 1024 bits to go-bitlist

Todos:

• Add tests for the new logic

[rauljordan]

Does this need to be a PR yet targeting develop? Or could it just live in its own branch for now?

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.