Ensure there is a consistent key for the session dict that will store the value of the poc_id if one is active.  If none is active, the mooc is assumed to be active.

Add mooc_name, mooc_url and active to the dict for each poc membership.

Update the navigation template to show link to mooc if poc is active, or to poc if not.

Ensure the switch_active_pocs view is covered well with tests.