Bug 1105976 - [Stingray][Home] Add Folder structure and its data access methods

https://bugzilla.mozilla.org/show_bug.cgi?id=1105976
Do you consider chaining `then` here? I think it's just too much indent here. Specifically,
```
return this._getPipedPromise(....) {
  ...  
  return that._cardStore.getData('cardList');
}.then(function(cardList) {
  ...
  var folderPromises = [];
  folderPromises.push(that._cardStore.getData(card.folderId));
  return Promise.all(folderPromises);
}.then(function(innerCardLists) {
  innerCardLists.forEach(function(innerCardList) {
    innerCardList.forEach(function(innerCardEntry) {
      ....
    });
  }
});
```
It's not blocking this patch though. But since we're using Promise, there should be a way to save us from indent hell.