Exchanges integration - additions

[andreibancioiu]

• return notarized blocks (not only their hashes)
• rename some API response fields (for full history)
• full history bugfix (get meta block by hash was not working)

How to test:

curl http://metachain-full-history-observer:8080/block/by-nonce/42
curl http://metachain-full-history-observer:8080/block/by-nonce/42?withTxs=true

And inspect the notarized blocks in the response.

curl http://metachain-full-history-observer:8080/block/by-hash/abcd...
curl http://metachain-full-history-observer:8080/block/by-hash/abcd...?withTxs=true

And inspect the response.

[LucianMincu]

System tests passed.