Order LoggingSystemFactory implementations more robustly

[wilkinsona]

The LoggingSystemFactory implementations are loaded using SpringFactoriesLoader. It orders them using AnnotationAwareOrderComparator but each LoggingSystemFactory implementation has the same order (Ordered.LOWEST_PRECEDENCE) which means the ordering is undefined. I think we're currently relying on SpringFactoriesLoader preserving the order of the comma-separated list in META-INF/spring.factories when parsing the file and then the sorting process leaving this order unchanged once the factories have been instantiated and their orders compared. To make things more robust, we should declare our LoggingSystemFactory implementations with orders that reflect our logging system preferences:

1. Logback
2. Log4j2
3. JUL