Add shortcut `Dataset.filter()` to avoid confusion with the `.query()` method

The requirement to call `Dataset.query().filter(field=value)` can be confusing. We can simplify this for most use cases by adding a `filter()` shortcut method to the Dataset object in the case where you do not need to provide additional query parameters. This would just call `self.query().filter(*args, **kwargs)` on the dataset instance.