TransactionId: implement Comparable<TransactionId> for use in ConcurrentSkipListMap

It is currently not possible to use this ID in a ConcurrentSkipListMap or any type of Concurrent Tree because it doesn't have Comparable. So I found a lexicographic comparison algorithm for byte[] and compare the ID bytes of the two objects, so it will work in these types of data structures one might need when implementing concurrent SCEP processing.