addDependency function on controllers to make it easier to add cleaned up things like events

[jemmyw]

class MyController extends ApplicationController {
  initialize() {
    // Dependency callbacks can be added next to the initialization code
    document.addEventListener("keydown", handleKeyDown);
    this.addDependency(() => document.removeEventListener("keydown", handleKeyDown));

    // observe is automatically cleaned up
    this.observe(() => { console.log(this.state.someValue); });

    // Dependencies can be named so they can be trigged any time
    const connection = new Connection();
    this.addDependency("close_connection", () => connection.close());
  }

  actionClose() {
    this.resolveDependency("close_connection");
  }

  handleKeyDown = (event) => {
  }
}