Jacks - Add Resources page: Check if the user is logged out

[innnkkki]

While at the Add resources page, if a user is logged out of the portal, he/she can still use jacks (draw a topology, etc) but the moment a button is pressed the user is send back to the login page, losing all the work that was done.

If it is possible, add a periodic check in the page that when the user tries to interact even with Jacks, he/she is sent back to the login page.

[tcmitchell]

See the fix for #1696 for an idea of how to handle this issue. Since Jacks calls out to the embedding page periodically with changes, we could grab a well-defined URL (hopefully one that already exists) and see if we get an expected response (i.e. JSON or XML) and if not, see if it looks like the discovery page. If we get the discovery page, then alert the user that their session has timed out.