Ctnr session variables now update when creating/deleting ctnrs.

As mentioned in https://github.com/OSU-Net/cyder/issues/60.
When a user deletes a ctnr, it is removed from their session ctnr list. If they were currently inside that contain, it resets them back to default. When a user creates a ctnr, that ctnr is added to their session ctnr list.