Intermediate commit, continuing work on Silva
Full accession id to NCBI taxon id map for Silva.
Revamped command loop to make --select preserve ids when there's only one input taxonomy.
Taxon ids are now arbitrary strings, not just integers (for Silva).
Source ids are now carried over from source taxonomies and edits into the OTT taxonomy file.
Add 'hybrid' as trigger for 'hybrid' flag.
Overhaul synonym processing to get more matches.
Add column to deprecated.tsv giving replacement ott ids for merged synonyms.
Revamp node matching rules again, for Silva.
Numerous internal changes.