Application users should have access to portfolio landing page.

- Adds override to portfolio landing page access check to see if user
  has access to any applications within the portfolio.
- Route for accepting an application invitation redirects directly to
  portfolio applications route.
- Tests ensure application user only sees apps the user has access to on
  the portfolio landing page.

templates/emails/application/invitation.txt

@@ -5,6 +5,6 @@
 Join this JEDI Cloud Application
 {{ owner }} has invited you to join a JEDI Cloud Application. Login now to view or use your JEDI Cloud resources.
 
-{# url_for("application.accept_invitation", token=token, _external=True) #}
+{{ url_for("applications.accept_invitation", token=token, _external=True) }}
 
 {% endblock %}