Bug 12176: [QA Follow-up] Small additem adjustments

Bug 12176: [QA Follow-up] Small additem adjustments

Adjusting a few small things and making qa tools happy:

[1] Remove .hidden after [% avalue %] in additem.tt. (Typo)
[2] A closer look revealed that mv.avalue is useless too. An input element
    does not contain any content. Putting it after the hidden element
    in a non-visible context has no meaning.
[3] Change handling of select attributes readonly and disabled.
[4] Remove unused variable $attributes_no_value_textarea
[5] Removed a comment with TODO referring to this report.
[6] Moving a duplicated TT variable (mv.javascript) outside IF statement.
[7] And finally could not resist this one: Moving strings Tag editor and
    No popup from script to template.  Plugins++
    NOTE: Most item plugins redirect click to focus. In that case there is
    no popup, but unfortunately the text Tag editor comes up.
    When you remove or rename function Click, No popup comes up. So it works.

Sorry that this small list kept growing :)

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>