Support/encourage using IB activity statements only, not activity + trades

[jspahrsummers]

bankroll-py/bankroll#35 introduces a query for activity statements, on top of the trade confirmation query recommended in the README. Activity statements can be configured to include trades in them, which might be a good idea because IB's Flex Query API is not very tolerant of multiple requests in succession.

On the other hand, maybe this increases the likelihood that they'll error out the query? Needs experimentation.

[jspahrsummers]

This will likely be complicated by the fact that Activity queries seem to (generally) take much longer than Trades.