Hy there fellas,

I've managed it on my own to it out.
But what cruel being would I be, if I don't share the answer with you.

1: Answer to this question:
var serviceObjectSprints = {
          self: this, //This you don't really need. But in this way you could iteract with the viewlet [this.self.test()]
          success: function(page) {
          },
          failure: function (error) {
          }
}
var srh3 = new ServiceResponseHandler(serviceObjectSprints, "success", "failure");
var args = {
       includeArchived: false, //Show archived too if true
       processAreaContext: 1, //IDK what's this for
       uuid: this.getScopeItem().itemId, //Place here the ProjArea UUID
};
ProcessClient.getProjectDevelopmentLines(args, srh3); //Returns an Object-Array with all Sprints in it

2: And with this construct you can get ALL(or the rest) of your Timelines:
args = {
       includeArchived: false,
       uuid: actualDevelopmentline.itemId,
};
ProcessClient.getIterations(args, srh4);