Allow for customizing the set of context graphs that are displayed for a particular dataset/scenario

[chrispcampbell]

Currently there is no way to filter out context graphs that are unrelated to a particular scenario. We have special comparison scenarios defined, and there are certain comparison graphs that are only relevant for one specific scenario, so we should be able to configure this.

(This is being split out from #539. See that issue for more background.)

[chrispcampbell]

I've added an optional method to the ComparisonDatasetOptions interface, which allows for overriding the default behavior.

export interface ComparisonDatasetOptions {
  // ...

  /**
   * An optional function that allows for customizing the set of context graphs
   * that are shown for a given dataset and scenario.  By default, all graphs in
   * which the dataset appears will be shown, but if a custom function is provided,
   * it can return a different set of graphs (for example, to omit graphs that are
   * not relevant under the given scenario).
   */
  contextGraphIdsForDataset?: (dataset: ComparisonDataset, scenario: ComparisonScenario) => BundleGraphId[]
}