Bug 26237: Move translatable strings out of preferences.tt and into JavaScript files

Bug 26237: Move translatable strings out of preferences.tt and into JavaScript files

This patch removes the definition of translatable strings out of
templates and into the corresponding JavaScript file, using the new JS
i81n function.

To test (a non-comprehensive list):

- Apply the patch, go to Administration -> System preference
- Modify any system preference. "modified" should appear next to the
  preference name.
- Click the "Save" button. You should get a message, "Saved preference
  <pref name>"
- Hover your mouse over a section heading (e.g. "Features" under
  Accounting). You should see a tooltip, "Click to collapse this
  section."
- Click to collapse the section. The tooltip should change to "Click to
  expand the section."
- Open a new tab for the staff interface and log out.
- In the original tab, modify and try to save a system preference. You
  should get a message, "Error; your data might not have been saved."

TESTING TRANSLATABILITY

- Update a translation, e.g. fr-FR:

  > cd misc/translator
  > perl translate update fr-FR

- Open the corresponding .po file for JavaScript strings, e.g.
  misc/translator/po/fr-FR-messages-js.po
- Locate strings pulled from
  koha-tmpl/intranet-tmpl/prog/js/pages/preferences.js for
  translation, e.g.:

  msgid "Saved preference %s"
  msgstr ""

- Edit the "msgstr" string however you want (it's just for
  testing).
- Install the updated translation:

  > perl translate install fr-FR

- Switch to your newly translated language in the staff
  client and repeat the test plan above. The translated strings
  should appear.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>