Expose anonymized order book in CoinffeineApp

**Description:** Expose anonymized order book in CoinffeineApp

Add an `openOrders` method to MarketStats (one of the traits composed
by CoinffeineApp) to do so.  Also, refactor `currentQuote` to be
consistent to the new method.

**Testing:** tests still pass.
**Coverage:** this is going to be used on an integration test after being ported.