Bug 7607: Remove empty inputs when submitting search form

Bug 7607: Remove empty inputs when submitting search form

This patch surrounds the operator, index, and query fields on the advanced search
page wtih a 'search_set' class.

This allows us to process them as a group and confirm the query is populated before submitting
the other parts to the form

TO test:
1 - Go to advanced search
2 - Use search boxes to search like:
    Title: (leave blank)
    Author: clinton
    keyword: shuffle
3 - Perform search
4 - Note no results as you searched for title:clinton etc.
5 - apply patch
6 - refresh and repeat
7 - search is now correct
8 - Try vaeious searches with 'more options' and selecting different operators

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>