also add delete multiple datastreams to the POST .../datastreams/ method.
refactoring out redundant classes
add setRepository method to make it easier to mess with the services' repository outside of spring (e.g. in poorly thought out tests.)
rename LowLevelCacheStore => LowLevelCacheEntry, and let it handle all the ISPN operations internally
make sure to log-out our repository initialization session
give FixityResult a readable toString output
create the (ugly) Datastream#runFixityAndFixProblems() method which will go in and fix up any fixity failures if possible.
add the LowLevelCacheEntry to the FixityResult.