Data structure for local BlockHeader metadata

[mercadoa]

Some operations require to store local meta-data about block headers.

For instance, for efficient synchronization it is needed to track the origin of block headers which have missing dependencies. Those can be store temporarily in a "staging" area, while missing dependencies are queried from their origin. This information can also be used to track sources of block headers that fail payload validation. Other useful information may include when a block header was first received, added to the database, and passed payload validation.

[mercadoa]

Moved issue over to chainweb-node (109)