Enforce hierarchy in clade assignments

[joverlee521]

This is a meta issue tracking all the way's we've tried to enforce hierarchy for clade assignments

• augur clades inheritance doesn't enforce inheritance augur#1837
• augur clades should assign clades hierarchically and parsimonously augur#1711
• Clade definition inheritance augur#1836
• Assign clades with Nextclade seasonal-flu#259
• https://github.com/neherlab/tidy-tree