Taxonomy compare via 'group duplicate search'

[westram]

Group duplicate search (as implemented in "Search groups" module) could help to compare taxonomies defined by groups in two different topologies:

• for all duplicate clusters containing exactly 2 groups from 2 different trees, a taxonomy mismatch penalty (XMP) could be calculated in the same way as done for "Move groups" (introduced with #780)
  • clusters with more than 2 hits cannot be compared due to ambiguous group names (e.g. meaningless for sth like 'uncultured')
• XMP could be used
  • to sort results (for taxonomy curation)
  • to exclude results from duplicate search (delete and retransfer groups; related #791)