Bug 28812: (bug 7882 follow up) Copy all subfields in plugin editor

Bug 28812: (bug 7882 follow up) Copy all subfields in plugin editor

To test:
1- Create a notice with a 700$a and 700$d
2- Click on 700 $a field Tag Editor
3- Only 700$a is copied in search windows eg /authorities/auth_finder.pl pop up
4- Apply patch
5- Redo 2
6- 700$a is copied in 'Search main heading ($a only)' and $d is copied in 'Search main heading'

Signed-off-by: George Veranis <gveranis@dataly.gr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit d35efbd1fbfd19f6fe4b3e5a924fe0c95cb4da13)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>