Bug 34574: Add CSS class to datatable select filter

Bug 34574: Add CSS class to datatable select filter

Test plan:

1) Create a new patron category, visit:
/cgi-bin/koha/admin/categories.pl?op=add_form
2) Add a category code, en enrollment period, a category type and a really long description like:
"This is a real long description of the patron category code for demo purposes"
3) Now do the same but for a library, visit:
/cgi-bin/koha/admin/branches.pl?op=add_form
4) Add a library code and a really long name like:
"This is a real long library name for demo purposes"
5) Visit patrons home:
/cgi-bin/koha/members/members-home.pl
6) Hit "Search". Notice the "library" and "category" columns grow in width to match the largest option (added in previous steps)
7) Apply patch, add the following CSS to IntranetUserCSS:
.dt-select-filter{
	max-width:200px;
}
8) repeat 5) and 6). Notice the columns no longer grow in width.

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 99014e9395c1811e6c9c31cbb781d77f49f05cc8)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>