KolabMailSideCache: rework of the previous gettext fix
KolabMailSideCache: rework of the previous gettext fix

* strdup() all strings returned by ngettext()
  to properly insert values for placeholders
* added better hints for translators to clarify
  that there are three separate but consecutive
  sentences, each translatable, which comprise
  one message

GNOME/evolution-kolab,GNOME/evolution-kolab