po: add missing translations in de, fr, it, zh

There are missing translations for the new "Copy" menu item.

The following people provided them to me on IRC just in time for the
QEMU 2.8 release:

 * de_DE - Stefan Hajnoczi <stefanha@redhat.com>
 * fr_FR - Laurent Vivier <laurent@vivier.eu>
 * it    - Pino Toscano <ptoscano@redhat.com>
 * zh_CN - Fam Zheng <famz@redhat.com>

[Removed spurious space in zh_CN "Copy" translation that Fam Zheng
pointed out.
--Stefan]

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20161214144713.11009-1-stefanha@redhat.com
Cc: Fam Zheng <famz@redhat.com>
Cc: Pino Toscano <ptoscano@redhat.com>
Cc: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

po/de_DE.po

@@ -46,7 +46,7 @@ msgstr "_Vollbild"
 
 #: ui/gtk.c:2032
 msgid "_Copy"
-msgstr ""
+msgstr "_Kopieren"
 
 #: ui/gtk.c:2048
 msgid "Zoom _In"

po/fr_FR.po

@@ -47,7 +47,7 @@ msgstr "Mode _plein écran"
 
 #: ui/gtk.c:2032
 msgid "_Copy"
-msgstr ""
+msgstr "_Copier"
 
 #: ui/gtk.c:2048
 msgid "Zoom _In"

po/it.po

@@ -42,11 +42,11 @@ msgstr "_Esci"
 
 #: ui/gtk.c:2029
 msgid "_Fullscreen"
-msgstr ""
+msgstr "A t_utto schermo"
 
 #: ui/gtk.c:2032
 msgid "_Copy"
-msgstr ""
+msgstr "_Copia"
 
 #: ui/gtk.c:2048
 msgid "Zoom _In"

po/zh_CN.po

@@ -47,7 +47,7 @@ msgstr "全屏(_F)"
 
 #: ui/gtk.c:2032
 msgid "_Copy"
-msgstr ""
+msgstr "复制(_C)"
 
 #: ui/gtk.c:2048
 msgid "Zoom _In"