Ensure every ajax request throws an error that end users can understand

Added new error messages to:
-1) assets/javascripts
 ---a) data_sets/
 ---b) news
 ---c) projects/
 ---d) shared/media_objects_view
 ---e) tutorials/show
 ---f) users/show
-2) lib/assets/javascripts
---a) content_edit_pane
---b) highvis/savedVis
---c) info_edit
---d) name_popup