NEXUS-7517: Added more logging and helpers

Added logging to the two central component (facade and storage)
and introduced log config helpers.

Changes:
* added logging to facade and NexusStorage
* added log config helper
* some minor cleanup re method and variable names

Issue
https://issues.sonatype.org/browse/NEXUS-7517

CI
http://bamboo.s/browse/NX-OSSF340