Bug 846768 - Switching apps is broken when we close another app before r=timdream

Several problems:
- we were decrementing twice the currentDisplayedApp value when closing using a
  swipe
- remove the useless callback in alignCurrentCard. We were not calling it in all
  situations before, but now I just removed it because we don't need to align
  before launching the app
(cherry picked from commit 3fdf72a6eb58be77cc3c2ee106e0dc98549ce87a)