fix!(aliby): dummy tiler object has shape attributes

WHY IS THIS CHANGE NEEDED?:
- it complained that ImageDummy object has no .shape attribute when
  Tiler methods like ._run_tp() were called

HOW DOES THE CHANGE SOLVE THE PROBLEM?:
- first argument of the object to be returned by .dummy() is mistakenly
  an Image instance (i.e. ImageDummy); it should be a dask array like
  those returned by e.g. .from_image(), .from_h5()
- fixed by using the .data attribute, consistent with the other methods mentioned

WHAT SIDE EFFECTS DOES THIS CHANGE HAVE?:
- order of dimensions is inconsistent: it is tczxy in io.image.py but
  ctzxy in the .shape() method in tiler.py.  this may break things down
  the line