[WIP] feat(aliby): base image class lazy-loads dummy image

WHY IS THIS CHANGE NEEDED?:
- need function that creates the expected output from dummy image file,
  as an interface for other classes' get_data_lazy() methods

HOW DOES THE CHANGE SOLVE THE PROBLEM?:
- create abstract method that loads the dummy image file and returns
  2d dask array
- define function to get examples directory, following logfile_parser.legacy

WHAT SIDE EFFECTS DOES THIS CHANGE HAVE?:
- only able to handle one TIF file (i.e. 1 z-section)

EVIDENCE THAT COMMIT WORKS:
- created a test class that extends BaseLocalImage and has a
  get_data_lazy() function that extends the base class's function; it is
  able to load the dummy image into a dask array

REFERENCES:
- issue #53