Webknossos

- Replaced the old properties classes of the Dataset API with attr-classes.
- The `Layer.rename()` function is now replaced with the setter of `Layer.name`.
- The functions `Layer.get_view_configuration` and `Layer.set_view_conficuration` are replaced by the property `Layer.default_view_configuration`. (Same applies to `Dataset.get_view_configuration` and `Dataset.set_view_configuration`)
- Moved `LayerViewConfiguration` and `DatasetViewConfiguration` into `properties.py`
- Removed `Layer.set_bounding_box_offset` and `Layer.set_bounding_box_size`.
- Renamed `Layer.get_bounding_box()` to the property `Layer.bounding_box`. The method `Layer.set_bounding_box` is replaced with the setter of the property `Layer.bounding_box`.
- Reverted that `dataset.add_symlink_layer` and `dataset.add_copy_layer` resolved the layer path if it was a symlink. [408](https://github.com/scalableminds/webknossos-libs/pull/408)

- Rollback `scikit-image` version from `0.18.0` to `0.16.2` because the newer version caused problems in voxelytics. [390](https://github.com/scalableminds/webknossos-cuber/pull/390/files)

- `dataset.add_symlink_layer` and `dataset.add_copy_layer` can now handle `Layer` arguments as well. The parameter `foreign_layer_path` was renamed to `foreign_layer`. [389](https://github.com/scalableminds/webknossos-cuber/pull/389)

- Bump scipy to 1.6.0 and scikit-image to 0.18.0 while keeping numpy to under 1.20.0 372
- Fixes a bug where modifications to an existing dataset with floats as dtype failed. 375