Bug 12576: Make the more/fewer options and "new search" links on the advanced search...

Bug 12576: Make the more/fewer options and "new search" links on the advanced search page look better.

How to test:
1/ Visit /cgi-bin/koha/opac-search.pl
2/ Assert the "More/Fewer options" buttons look like bootstrap default buttons
3/ Assert the "New search" button looks like a bootstrap default button
4/ Assert the visited colour of the buttons remains #333 (light grey)
5/ Assert the buttons still function as expected

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>