Reflect failure in list-of-links

[apetro]

When list-of-links widgets fail (e.g. because remote JSON defining links fails), reflect that failure appropriately to user or otherwise fail more sensibly than as a blank tile.

(Screenshot doesn't exactly match this client-side error log, but you get the idea.)

Error: links is undefined
widgetType/<@https://test.my.wisc.edu/web/portal/widgets/controllers.js:46:21
e/<@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:131:20
$eval@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:145:343
$digest@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:142:412
$apply@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:146:111
l@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:97:320
J@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:102:34
gg/</t.onload@https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js:103:4
angular.js:13920:17
List of links widget HRSManagerTimeApproval failed.