Add the possibility to specify business calendar outside the class path

The system property jbpm.business.calendar.properties expects a file location in the classpath, eg. below ${RHPAM}/standalone/deployments/kie-server.war/WEB-INF/classes. This is not useful in OCP as it would require a change of the image instead of pointing to a location somewhere on a mounted volume.

The loading of the properties file should work in the classpath context to ensure backwards compatibility, but also for external locations.