Implement :class:`mne.decoding.SpatialFilter` class returned by :func:`mne.decoding.get_spatial_filter_from_estimator` for visualisation of filters and patterns for :class:`mne.decoding.LinearModel` and additionally eigenvalues for GED-based transformers such as :class:`mne.decoding.XdawnTransformer`, :class:`mne.decoding.CSP`, by `Gennadiy Belonosov`_.