Fixing folder focus logic

> Folder items no longer remain in a linear order when a folder
gets rearranged, and se we need to use createSparseMatrix instead
of createFullArray. Also because of this we need to use getChildAt(x, y)
instead of getChildAt(index)
> Removing traces of AppsCustomizePage (all apps) from FocusHelper

Change-Id: I9007f6b95cb823e27ef4a43ce725fda8ef1b7cf8