First version: show all open bills
Test
openBills test working when run separate
Fixed test
Merge remote-tracking branch 'origin/technical/fixunittests' into
develop

Conflicts [solved]:
	oscr/oscr-business/src/test/java/de/bstreit/java/oscr/business/bill/BillTestFactory.java
	oscr/oscr-gui-swing/src/main/java/de/bstreit/java/oscr/gui/swing/cashregister/ui/factories/ButtonPanelFactory.java