Fix i18n of strings on auth group add/edit pages

[seanh]

There are a couple of strings on the authorization group add/edit form that are not being translated:

"Name: Please enter a value" (error message when you try to add an auth group with no name)

"User name"

"Save" button

The form seems to be built using FormBuilder?. See ckan/forms/authorizationgroup.py, builder.set_displayed_fields()

[ross]

Auth groups are being deprecated