[TIME-80] Portlet cannot be used as gadget in Confluence

Although the gadget-that-is-the-portlet does show in a JIRA 4 Dashboard, it does not work in a Confluence page. The screenshot shows that we only see a blank rectangle during setup, and in the page.

The gadget URL used is

{gadget:url=https://HTTPD-PROXY-DOMAIN-NAM/jira/rest/gadget/1.0/legacy/spec/com.fdu.jira.plugin.timesheet:portlet.xml|width=1000}