Another iteration of GO adaptor.
Another iteration of GO adaptor.

- Allow to specify a translation for "localhost", through config or
  environment.
- Handle errors from CLI commands and translate into SAGA Exceptions.
- Add exists() to Directory().
- Add a stat() function that is used by get_size(), exist(), is_dir(),
  is_file() and is_link().
- Use stat() during initialization of File() and Directory().
- get_go_endpoint_ids() doesnt return hostname anymore (was not used).
- Remove some unused calls to get_go_endpoint_ids().
- Some more TODOs left behind.

luis-rr/saga-python,luis-rr/saga-python,telamonian/saga-python,luis-rr/saga-python,mehdisadeghi/saga-python,telamonian/saga-python,mehdisadeghi/saga-python