ENH: Allow export/import of collections as JSON or YAML

[corneliusroemer]

I was wondering if it was possible to save the work we do on collections in case something happens, e.g. compromised password or outage etc.

Once export works, one could also do import.

That may also open the door to auto-generated collections, e.g. one could quickly programatically create a collection for all pango lineages etc.