[x] authenticated users may access any object (note: assume for now that objects in the Tufts production Fedora do not have access controls implemented)
[x] only objects with displays includes 'tdil' should be shown in the application
[x] unauthenticated users should not be able to access collections or images (see #22)
@jcoyne mentioned that we shouldn't use displays_tesim to filter the search because _tesim might match other objects with teh same stem, so we should switch it to _ssim instead.