Integrate real-time view of deals and piece index to Spark

[bajtos]

After completing the Spark Piece Indexer (#143, #194) and Real-time view of all storage deals (including DDO), we need to rework Spark to use these new features.

• Design proposal for Spark v2 as the first Checker Network module (keep Spark v1 running alongside)
• Rework the way how spark-api picks deals to test in a given round
• Rework the definition of a task to (minerId, pieceCid, pieceSize)
• Rework the checker to resolve (pieceCid,pieceSize) to payloadCid using the piece indexer
• Rework spark-evaluate to accommodate these changes
• Write a blog post announcing the changes and explaining the new retrieval testing workflow

Links:

• Spark v2 Design and Migration