Bug 8549 - DataTables upgrade broke display of next/previous buttons in table controls

Bug 8549 - DataTables upgrade broke display of next/previous buttons in table controls

When the DataTables plugin was upgraded the DataTables CSS
was not updated at the same time, causing problems in the
display due to changes in how the plugin works.

The DataTables upgrade added text lables to the image-only
buttons in order to improve accessibility. This patch
revises the CSS and the four_button pager modification
to conform with the upgrade.

To test, please view tables which use each of three types of
pagers: default two-button (ex: circ/pendingreserves),
custom four-button (ex: members/readingrec.pl) and full
(ex: tools/quotes.pl).

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>