erp5_trade, OrderModule_activateGetOrderStatList: make at_date inclusive

The way it was in reports involving OrderModule_activateGetOrderStatList, at_date was not included. There even was a mis-match of assigning:

to_date = request.get('at_date', None)

One commit to fix this including also some formatting fixups.

Second commit adding a test-case in testTradeReports, where a report is run having at_date as the start_date of a Sale Order. Previous code would fail in this, since the Sale Order was not considered in the report.