Refactor to decorators

[Lodin]

Refactor whole project to use decorators as a preparation to upcoming decorators proposal. Unfortunately, due to decorators unability to change class type some typings became more complex to use. E.g. to use routeResolving of @outlet it is necessary to cast class to any:

@outlet(routes)
class RouterOutlet extends HTMLElement {
  public async waitForRouterResolving(): Promise<void> {
    await (this as any).routeResolving;
  }
}