Webknossos

- After downsampling data, the bounding box gets saved correctly to the `datasource-properties.json`.

- Updates the usage examples in the `README`
- Relaxes the constraint that all input files need to have the same type when auto-converting
- The interface for `downsampling` was completely reworked. The flags `anisotropic_target_mag` and `isotropic` are now deprecated. Use `max` and `sampling_mode` instead.

- Fix PEP 561 compatibility

- The dataset API now interprets `float` as 32bit. `double` can be passed as a string to use a floatingpoint with 64bit as dtype (specifying the dtype explicitly, e.g. `np.float64`, still works). The `datasource-properties.json` stores 32bit floats as `"float"` and 64bit floats as `"double"`. [316](https://github.com/scalableminds/webknossos-cuber/pull/316)

- The file `py.typed` was added to tell `mypy` to check this package if it is used in other projects

Uses a newer cluster-tools version which fixed a bug when submitting empty jobs.