Prepend context path to job page URLs

When linking to individual job pages in the XF panel view, the generated job page URLs are missing the context path, i. e. they are relative -- and thus lead to non-existing pages, giving the user a "404 Not Found" page. This pull request fixes that by prepending [`rootURL`](https://wiki.jenkins-ci.org/display/JENKINS/Hyperlinks+in+HTML) to the job page URLs.