Add support to select the location from the userProperty in the Login Screen

The reference application has the feature to select the session location in the login page. It would be good to add support to select the user location through the userProperty(if only available), and hide the location selector in case of this feature available.

Dev Notes 

Track this feature with a global property as "referenceapplication.locationUserPropertyName", if this global property exists in the system or has any value, then hide the location selector in the login screen, and fetch the session location from the user property using that user property name.

Work needed here : https://github.com/openmrs/openmrs-module-referenceapplication/blob/master/omod/src/main/java/org/openmrs/module/referenceapplication/page/controller/LoginPageController.java#L187