STY : cleaned up Import.xtomo_reader

 - explicitly use slices via `slice` object rather than implicitly
   (via [start:stop:step])
   - this removes the need for setting defaults to the size
 - added @staticmethod to methods that are static.

 - Import should really be a module, not a class.

 - buckets of pep8 add `?w=1` to the url to suppress seeing white space changes. (https://github.com/blog/967-github-secrets)