If we could set a grapher-specific configuration object for each metric, I think it would only need to specify

- Grapher#graph
- Grapher#build_data method
- graph_element (canvas vs. div)
- js file locations
  - header tags
  - footer tags
- css styles

Right? 

There had been a distinction between 'bluff' and 'google_charts' for a while, but I removed the latter for maintainability reasons.