Implement architecture for component JS to talk to other component JS

[anselmbradford]

Current behavior

• Components are initialized within their package scope, such as on here, so don't provide an opportunity for other components to listen to events on them or to call methods on their API (such as show/hide or whatever).

Expected behavior

• Particular components are able to listen to events on other components and call public methods on those other component's API.

[anselmbradford]

Related to https://github.com/cfpb/capital-framework/issues/667