* Add headers with proof content type and use it for verification
- Add BlockHeaderWithProof content type & content
- Use BlockHeaderWithProof content to verify if chain data is
part of the canonical chain
- Adjust parser & seeder code to be able to seed these headers
with proof
- Adjust eth_data_exporter to be able to export custom header
ranges for which to build proofs (mostly for testing)
There is currently quite some ugliness & clean-up needed for which
a big part is due tos upporting both BlockHeader and
BlockHeaderWithProof on the network.
* Change accumulator proof to array / SSZ vector type
- Change accumulator proof to SSZ vector instead of SSZ list.
- Add and use general buildProof and buildHeaderWithProof func.
* Make the BlockHeaderWithProof an SSZ Union with None option
* Update portal-spec-tests to master commit
Kim De Mey
KonradStaniec