Bug 28934: Make the OPAC registration form design consistent

Bug 28934: Make the OPAC registration form design consistent

The gender/sex and GDPR inputs were slightly misaligned (by
1.5em). Now they are aligned with the other inputs which have a width
of 10em (9em width + margin 1em). The label assignments and required
attributes for input elements are made also consistent.

To test:
 1) Enable GDPR_Policy syspref
 2) Apply patch, run "yarn build --view opac", restart plack
 3) Go to /cgi-bin/koha/opac-memberentry.pl
 4) Check that the GDPR input box shows the required text now in red
    color
 5) Check that the alignment of sex/gender and GDPR input matches with
    the other inputs perfectly.

Signed-off-by: Hayley Pelham <hayleypelham@catalyst.net.nz>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>