[JENKINS-21204] Add ability to boost recently failed Jobs

Added new PriorityStrategy called HealthStrategy
Refactoring of the Item logging.
[JENKINS-21284] Add some logging to show what the sorter is doing

Now logging number of sorted items on FINE after sorting
[JENKINS-21289]	Item Logging causing NPE

getLevel() return <null> when no logger is configured.
Merge pull request #13 from emsa23/master

Towards 2.5