Need BTi example for MEG datasets

[sappelhoff]

Currently, there is no MEG dataset in the examples that contains correctly saved BTi data. This is problematic, because we cannot adequately catch errors that come about while the development on the bids-validator continues.

As an example for this problem, see: https://github.com/INCF/bids-validator/issues/553

Somebody familiar with the BTi format should take some time and prepare a simple example. One possible option would be to use the tutorial data shipped with MNE-Python:

https://mne-tools.github.io/dev/generated/mne.datasets.phantom_4dbti.data_path.html#mne.datasets.phantom_4dbti.data_path

@jasmainak @robertoostenveld

[sappelhoff]

Closing, because the urgency I felt when opening this issue has completely waned.