transactions and orders as standalone events
- added transaction and order types
- moved TransactionSimulator from trading.py to tradesimulation.py
(only used by other members of the tradesimulation module)
- made transaction an independent event, like dividend

added Blotter
- flattened the transaction events to be independent
- made orders into events that reach performance (need to add
handling)
- issueing IDs to orders and tracking each transaction's order id.
- made volume share slippage fill orders independently, rather than
aggregating them into a single transaction.
- perf tracker now holds orders, serializes them with transactions.
patched minute test to use independent transaction events.
order state defined and maintained by the order.
minutely emission of orders based on last_modified date.
added to_python methods to transaction and order for emitting dict
- implementation uses a copy, deletes fields that aren't meant for
downstream consumers

fixed bug in rollover of orders. Open orders are retained.
renaming method to be the more quasi-standard to_dict
fixed dividend tests to use Transaction objects.
renamed Order's last_modified to last_modified_dt
fixed minute test to work with order and transactions
as independent events.