if you create a new Todo, you have to add in which set you want to add the new Todo:
e.g.:
var t = new Todo({name: "go to school", today: "2016-04-26"});
will add a new Todo in the set => today: 2016-04-26
if you want also the displayed list sorted so have to specify a set.comparators.sort(). You need to request a sort-set var todoPromise2 = Todo.getList({today: "2016-04-26", orderBy: "name"});.