Bug 12176: Remove HTML from additem.pl

Bug 12176: Remove HTML from additem.pl

This patch removes HTML code from additem.pl.

To test:
1. Check no regressions on Add/Edit/Save items
2. Update translation files for a language,
   check new strings "Tag editor" & "No popup" on staff PO file
3. Check it passes xt/tt_valid.t

Patch partially rebased, part rewritten.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
(cherry picked from commit 47d2de9c024bfb93d56184f298f334b20685cd86)
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>