add mappings for snRNA and snoRNA

git-svn-id: svn+ssh://svn.internal.sanger.ac.uk/repos/svn/pathsoft/artemis/trunk@16395 ee4ac58c-ac51-4696-9907-e4b3aa274f04

etc/key_mapping

@@ -21,3 +21,5 @@ direct_repeat                              repeat_region   rpt_type=direct
 polypeptide_domain                         misc_feature
 centromere                                 misc_feature    note=centromere
 modified_amino_acid_feature                misc_feature    note=modified_amino_acid_feature
+snRNA                                      ncRNA           ncRNA_class="snRNA"
+snoRNA                                     ncRNA           ncRNA_class="snoRNA"