Changes:
  - Added scope="col" to table header tags <th> that were missing them.
  - The Jquery dropdown menus in tables are closed when the table cell
containing it is out of focus.

(The issue the fontawesome sort icons are read as 'column # link'.
Add some screen reader only text. This issue was sorted by someone else
who added ".screen-reader-text" class to the sort_link_name() method in
app/controllers/concerns/paginable.rb.)

Fix for issue #1455.