Support reads without readgroups
Support reads without readgroups

- give those reads a default sample of “unknown”
- also sort readsets so they get ids in a predictable order
- fixes #8

mbookman/api-client-python,mbookman/api-client-python,hanv89/api-client-python,hanv89/api-client-python,hanv89/api-client-python,mbookman/api-client-python