Merge pull request nextstrain#640 from nextstrain/support-default-gis…

…aid-metadata

Support default GISAID metadata and sequences

Update change log for v6 release

Merge pull request nextstrain#615 from nextstrain/drop-backward-compa…

…tibility

Drop backward compatibility

Merge pull request nextstrain#605 from nextstrain/support-gisaid-down…

…loads

Support GISAID downloads

Merge pull request nextstrain#592 from nextstrain/global-context

Enable workflows based on curated global context sequences

Merge pull request nextstrain#596 from nextstrain/add-change-log

Add change log

Remove references to "geographic_scale" from docs

We no longer require a "geographic_scale" attribute.