Bring back signature line context menu items

They were removed with fa39a342

Change-Id: I4a717cc9e4ec11dcd3980d8a7f37511417175da7
Reviewed-on: https://gerrit.libreoffice.org/62948Reviewed-by: andreas_kainz <kainz.a@gmail.com>
Tested-by: andreas_kainz <kainz.a@gmail.com>
Tested-by: Jenkins
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>

sc/uiconfig/scalc/popupmenu/graphic.xml

@@ -65,4 +65,7 @@
   <menu:menuitem menu:id=".uno:DeleteShapeHyperlink"/>
   <menu:menuitem menu:id=".uno:OpenHyperlinkOnCursor"/>
   <menu:menuitem menu:id=".uno:AssignMacro"/>
+  <menu:menuseparator/>
+  <menu:menuitem menu:id=".uno:EditSignatureLine"/>
+  <menu:menuitem menu:id=".uno:SignSignatureLine"/>
 </menu:menupopup>