optimize TxReport (resolves performance bug)

This commit solves a major performance bug with respect to TxReport. This was particularly noticeable when transacting significant volumes of data, as the contents of the transaction report was being eagerly wrapped into Scala data structures, and thus generating vast amounts of garbage.
Merge pull request #85 from pellucidanalytics/topic/optimize-tx-report

Optimize TxReport (resolves performance bug)