move org.sonatype.nexus.log -> nexus-log-api module
Extract nexus-log-api into module, move impls to org.sonatype.nexus.internal.log
Update location of default logback.properties resource
Move non-framework event shit to org.sonatype.nexus.events
NX-506: switch to Hibernate Validator
Merge pull request #580 from sonatype/extract-nexus-log-api

REVIEW: Extract nexus log api
Merge branch 'master' into remove-notifications

Conflicts:
	plugins/rapture/nexus-coreui-plugin/src/main/java/org/sonatype/nexus/coreui/NotificationSettingsComponent.groovy