[NEXUS-6079] Add button allowing reset of all loggers to their default levels

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
update icon, add spacer, update text
Merge remote-tracking branch 'origin/master' into NEXUS-6079-reset-loggers
Merge pull request #226 from sonatype/NEXUS-6079-reset-loggers

REVIEW: [NEXUS-6079] Reset loggers