Make order book to have multiple orders per requester

Also, split it into OrderBook and OrderMap and decouple it from
exchange id generation.
Merge pull request #140 from sortega/feature/order_book

Make order book to have multiple orders per requester
Update version of Scala and dependencies
Enable another acceptance test
Merge pull request #142 from edrevo/general-update

Update version of Scala and dependencies
Merge pull request #143 from edrevo/enable-acceptance-test

Enable another acceptance test