Implement proper partitioning by day and purge
make monitor object final
Merge remote-tracking branch 'origin/master' into finish-timeline-partitioning
Merge remote-tracking branch 'origin/master' into finish-timeline-partitioning
Bugfix, improvements and comments

Fixed a bug about purge ;)
Improved "day change" detection to go only "forward" not
backward, as in case of async even processing and at midnight
this would introduce "oscillations" in partition creation. now
the part is only switched once.
Added some explanation to purge related to KZ
Added UT for partitioning by day
Merge remote-tracking branch 'origin/master' into finish-timeline-partitioning
Applied Stuart comments.

Also, improved UT to make sure that record we
expect to exists is still there
removed unused import and unneeded catch
Merge pull request #544 from sonatype/finish-timeline-partitioning

NEXUS-6615: Implement proper partitioning by day and purge