add literature qualifier

git-svn-id: svn+ssh://svn.internal.sanger.ac.uk/repos/svn/pathsoft/artemis/trunk@12443 ee4ac58c-ac51-4696-9907-e4b3aa274f04

etc/options

@@ -564,6 +564,7 @@ extra_qualifiers_gff = \
     GO "text" \
     isFminPartial none \
     isFmaxPartial none \
+    literature "text" \
     note "text" \
     orthologous_to "text" \
     paralogous_to "text" \