Origin block store should exist in a minimal version

[schemar]

The base BlockStore should track all blocks and verify the parent hashes (not only the auxiliary block store).

The base block store should verify that votes are targeting a child of the source (same blockchain).

The origin block store only stores block reports - which it inherits from the base block store - and it returns a origin transition object and hash.

The block store should not require the starting block hash in the constructor. The origin block store should get the hash in the constructor.

The auxiliary block store should have an init() function (or extend it if it exists) that requires that the starting block hash is 0x00... and then sets it to the block hash it gets from the solidity built-in method (the current block hash).

Only the auxiliary block store will be able to verify block hashes against the most recent 256 known hashes.

Casper messages are part of both (base class).