LGTM.com - false positive - unused import needed for API

**Description of the false positive**

`Unused import` raised for imports that are carried out just to build the API-structure.

**URL to the alert on the project page on LGTM.com**

- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/_lazy_signals.py?sort=name&dir=ASC&mode=heatmap#xb0feefedc9751814:1
- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/drawing/widgets.py#x7c61e9e86d08ba4e:1
- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/io_plugins/hspy.py#xfe443ac8dbb99926:1
- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/misc/machine_learning/import_sklearn.py#x10662ea808f30f82:1
- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/samfire_utils/fit_tests.py#x5f531cee568f309c:1
- https://lgtm.com/projects/g/hyperspy/hyperspy/snapshot/508d6caf0efc5c0a258c67f5c2ecab8a977c413e/files/hyperspy/datasets/example_signals.py#x1c59a584f5028d6a:1