Refactoring of setting app starting window code.

This improves the code in following ways:
* move transferring of starting window into a separate method, so it can
be easier to understand;
* move checking of whether to display starting window from phone window
manager to window manager service; this has three benefits:
  1) whole logic is in one place;
  2) we don't need to schedule addition of a starting window, if we
     would stop it later anyway;
  3) we don't need to wait for creation of window style to decide, if a
     window is floating.

Change-Id: Ibfbd87b84a7080e372211f162fa1865f8c5ab973