P300 annotations

[Sara04]

This PR fixes the problem with the annotation loading for the P300 datasets Sosulski2019, Huebner2017 and Huebner2018.

[sylvchev]

You could use pre-commit to apply black formatting on your code and this is good to merge!

[Sara04]

Thanks, @sylvchev !
There was still the problem with passing dict as a default argument since it is mutable data structure, so I've changed:
from
description_map = {"Stimulus/S 21": "Target", "Stimulus/S 1": "NonTarget"} (in class init arguments)
self.description_map = description_map
to
self.description_map = {"Stimulus/S 21": "Target", "Stimulus/S 1": "NonTarget"}

[bruAristimunha]

Thank you @Sara04 and @sylvchev!