Fixed SAPUI5 compatibility+usability issues in web shop app

* Issue-01 Web Shop - Country selection: use sap.ui.core.ListItem instead of sap.ui.core.Item, Required according to doc (v. 1.12.1): https://sapui5.hana.ondemand.com/sdk/#docs/api/symbols/sap.ui.commons.ComboBox.html#addItem

* Improvement-01 Web Shop - DateTimePicker only shows -10/+10 years to current year --> Insufiecient to select year of birth!