Drop notifications api, this was used only for auto-[un]block notifications.
Merge branch 'master' into remove-notifications

Conflicts:
	plugins/rapture/nexus-coreui-plugin/src/main/java/org/sonatype/nexus/coreui/NotificationSettingsComponent.groovy
Merge pull request #582 from sonatype/remove-notifications

REVIEW: Drop org.sonatype.nexus.notifications api