Bug 37781: Add translation context for "On" (when used alone)

Bug 37781: Add translation context for "On" (when used alone)

This patch adds context to the string "On" used alone in the item search
page, to mean "On a specific date".

To test:
1. Update translation files

gulp po:update --lang fr-CA

2. Check the staff-prog.po file and search for "On".

vi misc/translator/po/fr-CA-staff-prog.po

/"On"

   --> It should be in three places, two in itemsearch.tt and
       one in smtp_servers.tt

 #. For the first occurrence,
 #. SCRIPT
 #: koha-tmpl/intranet-tmpl/prog/en/modules/admin/smtp_servers.tt:327
 #: koha-tmpl/intranet-tmpl/prog/en/modules/catalogue/itemsearch.tt:322
 #: koha-tmpl/intranet-tmpl/prog/en/modules/catalogue/itemsearch.tt:324
 #, c-format
 msgid "On"
 msgstr "Sur "

3. Apply patch
4. Reupdate po files

gulp po:update --lang fr-CA

5. Check the misc/translator/po/fr-CA-messages.po file and search for "On"

    --> There should be a msgctxt line that adds context to the
        "On" (please ignore the translated msgstr, I have no idea
        how it decides what to put in there!)

 #: koha-tmpl/intranet-tmpl/prog/en/modules/admin/smtp_servers.tt:404
 #, fuzzy
 msgctxt "Active"
 msgid "On"
 msgstr "Oman"

 #: koha-tmpl/intranet-tmpl/prog/en/modules/catalogue/itemsearch.tt:322
 #: koha-tmpl/intranet-tmpl/prog/en/modules/catalogue/itemsearch.tt:324
 #, fuzzy
 msgctxt "On specific date"
 msgid "On"
 msgstr "Oman"

6. Also check the item search page
   --> It should still work and the "On" in the last borrowed date
       drop-down should still say "On"

7. In the SMTP servers page, add a server and enable the "Debug" mode.
   --> In the list of servers, the Debug column should still say simply
       "On"

8. Optionally, translate the string and remove the "#fuzzy" line,
   install the translation and check the item search page
   --> It should use the string you put in

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