Support resource domain

As of JENKINS-41891 in Jenkins 2.200, the way this plugin works is undesirable—much too complex, and not very functional. It should merely copy the selected files to htmlreports and then serve them via DirectoryBrowserSupport (using target="_blank" so as not to lose track of the Jenkins site) without further mutilation. No BaseHTMLAction/index, no htmlpublisher-wrapper.html generation, etc. Ideally this would be done automatically when ResourceDomainConfiguration.isResourceDomainConfigured, though currently this is a @Restricted API.