Added API for Long-Lived Transactions.
LongTx

  * Also added a better 'toString' to the VBox class
Cannot use BPlusTrees in LogEntries
The transaction backing a Long Lived Transaction must allow writes.

  * Also, added support for Read-Only steps of Long Lived Transactions
Minor Change: Simplified DML, added utility methods to add LogEntries
Persist write-set, take 1
JSON
Added LogEntries cache.
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