Bug 25476: Add ability to browse file uploads by category

Bug 25476: Add ability to browse file uploads by category

This patch adds the ability to search/browse files by category.
(Note it doesn't include temporary uploads since they don't have
 a "category" per se.)

Test Plan:
0) Apply patch
1) Go to /cgi-bin/koha/admin/authorised_values.pl
2) Create "UPLOAD" authorized value category
3) Create "test" authorized value in "UPLOAD" category
4) Go to /cgi-bin/koha/tools/upload.pl
5) Note "Search uploads by category" fieldset
6) Upload new file to "test" category
7) Click "Back"
8) Choose "test" category in "Search uploads by category"
9) Click "Search"
10) Note that your file upload is displayed in result list

Signed-off-by: Mazen Khallaf <mazen.i.khallaf@gamil.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>