Bug 16322 - Translatability: "Unknown" in suggestion/suggestion.pl not translatable

Bug 16322 - Translatability: "Unknown" in suggestion/suggestion.pl not translatable

This patch adds translatability for the tab "Unknown" in
koha-tmpl/intranet-tmpl/prog/en/modules/suggestion/suggestion.tt

To test:
- Apply patch
- Examine koha-tmpl/intranet-tmpl/prog/en/modules/suggestion/suggestion.tt
  and verify that it handles the label "Unknown" (line 496)
- Go to suggestion/suggestion.pl, set status of a suggestion to -- Choose a status --
  and verify that the tab "Status unknown" appears
- Bonus test: Go through a translation process and verify that "Status unknown" is
  translated

Note: If you have a suggestion with unknown status, all suggestions are listed under
      this tab. This is not in the scope of this bug; this bug is about translation
      only.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as expected

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit d4819505971c6e7f1ce5f1017eddbbcf25254fea)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>