Mock ingest transactions & produce blocks

[karlfloersch]

The aggregator must accept transactions, and produce blocks with state updates which result from those transactions. This process is independent from the authentication of transactions or the state transition calculations. Therefore we can create an initial version which simply accepts transactions with ingestTransaction() where the transaction is simply the StateUpdate which will be included in the next block. These StateUpdates will be added to a queue which is then emptied periodically to produce a next block.

The function calls would look something like:

• generateNSequentialStateUpdates() https://github.com/plasma-group/pigi/blob/master/packages/core/test/app/block-production/merkle-interval-tree.spec.ts#L19-L38 on the client. Then send those state updates to...
• ingestTransaction(transaction) on the aggregator (right now transactions are just state updates). This would mock executeTransaction() and simply push the SU to...
• enqueueStateUpdate(StateUpdate) which adds our StateUpdate to a RangeBucket (eg. https://github.com/plasma-group/pigi/blob/master/packages/core/test/app/db/range-bucket.spec.ts#L160 )
• produceBlock() which is triggered periodically that first checks if there are stateupdates in the queue (our rangeDB bucket), and then produces a block if this is true.

Some of this functionality was started in -- https://github.com/plasma-group/pigi/pull/280/files .