Component Manager + Stacked Area Graph (NOT READY)

- Added a `stack` data selection to derive new data in stacked format.
- Many assumptions related to sequence are made in graph.js. This needs to be refactored out.
- The majority of graph.js deals with managing components. This should be extracted into a separate module b/c this functionality will be used by individual components (which contain sub-components) and other visualization types.
- Component configuration and structure should be serializable for saving graphs and making config easier.
- Reach-specific component configuration should be isolated to the graph-builder for now.