Ground-up rewrite of session timeout script; style tweaks to some admin ui elements.

src/main/webapp/WEB-INF/tags/page/xnat.tag

src/main/webapp/page/admin/style.css

src/main/webapp/scripts/xmodal-v1/xmodal.js

src/main/webapp/scripts/xnat/app/timeout.js

src/main/webapp/scripts/xnat/ui/panel.js

src/main/webapp/scripts/xnat/ui/templates.js

src/main/webapp/xnat-templates/navigations/DefaultTop.vm