title: Define an API endpoint in Angular2 (typescript)
body: <p>I am very new in Angular2.
  I would like to have a single class having all my API endpoints (allowing parameters and such in the different routes) that I could inject in all my services.
  What's the best way to do so in Angular2. I mean, should I define an <code>@Injectable class</code> as you would do when defining a service (and then add it to my services'<code>PROVIDERS</code>) or is it something similar to <code>constant</code> in angular 1.x that I could use</p>