[#1976108] by jthorson: Allow metadata types to flag that they should not be considered a sort-by candidate

Jeremy Thorson authored Apr 21, 2013 and Derek Wright committed Apr 21, 2013

Previously, hook_extended_file_field_widget_item_alter() was called
separately for each item. Now it's a single call for all files.

- UI cleanup for the new widget setting for which metadata to display
- Fixed a PHP notice if the metadata columns haven't been configured
- Fixed a now-stale comment in the API docs
- Fixed some PHPdoc typos

Signed-off-by: Jeremy Thorson <jthorson@sasktel.net>

This adds an 'Administer file attachments' permission. Any users with
that permission always see the remove button, even if the widget is
configured to hide it.

Commit 31d648af missed one case for renaming the setting (since I
forgot to search/grep in extended_file_field.theme.inc).

Any hook_preprocess_TEMPLATE() function that's preprocessing some
other module's theme template needs to live in the .module file for
the theme system to find it.  hook_theme() doesn't help us.

Checkboxes that you enable to hide something are confusing. Now, the
setting reads: [x] Show the 'Remove' button when editing files.