[keycloak-dev] Added 'keycloak.jsonPrettyPrint' system property

I fixed an issue where lists of json representations included null values (basically the configuration was just included for packages that started 'org.keycloak' which java.util.List isn't). At the same time I added a system property 'keycloak.jsonPrettyPrint' if enabled Keycloak will return pretty printed json which is nice for development/debug.