Bug 22195: (follow-up) Add text labels to buttons if window is wide enough

Bug 22195: (follow-up) Add text labels to buttons if window is wide enough

This patch adds responsive handling of text labels to the columns
configuration and export buttons.

To test, apply the patch and clear your browser cache if necessary.

 - View a page with column configuration, e.g. Administration -> Patron
   categories.
 - At wider browser widths the buttons should have text labels.
 - At narrower browser widths the labels should be hidden.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>