Implement IAppStore in portal core to store IApp by user session.
Implement and expose IPortalService to give an OPA the possibility to
retrieve it's IApp built by the Portal.
Configure OPA Hello to retrieve its IApp.
Configure osgi-portal-web to render the IApp iframe with the signature
in the HTTP request params.
Add tomcat context.xml in OPA header to share the session between IApp
ant portal.