Add JSON support to Nexus client

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge remote-tracking branch 'origin/master' into nexus-client-json
NEXUS-5472: Too chatty on INFO

Lowering the log level to DEBUG, as WL on
an ordinary day might become too chatty.
Fix requirejs error handling
Merge pull request #729 from sonatype/nexus-client-json

Add JSON support to Nexus client
Exposing ruleA and ruleB settings
NEXUS-5472: Improve scrape message
NEXUS-5472: Proper merge implemented

PRevious implementation did "equality" check, but that's not good
when both, child and parent path are about to be merged.
NEXUS-5472: Adding more comments

And fine tune how matching node is built
NEXUS-5472: UT for merging ES
NEXUS-5472: License hdr for new UT
NEXUS-5472: Unpublish repo while being updated in bg

For longer updates (remote scrape) this is a must, to prevent
downstream Nxes to scrape this repo while a potentially long running
upstream scrape is underway.
Merge remote-tracking branch 'origin/master' into nexus-5472-proxy404