consistent dataset-derived key names

[ChristopherBarrington]

and same for stages

[ChristopherBarrington]

Use:

• {stage,dataset}_key: entry name from yaml, used as default for other entries
• {stage,dataset}_name: can be space separated name, used for reports and tags
• {stage,dataset}_id: directory/filename-safe, used for outputs
• {stage,dataset}_tag: an abbreviated identifier

[ChristopherBarrington]

done #24