Add Thielen2015 c-VEP dataset

[thijor]

This pull request adds the Thielen et al. 2015 c-VEP dataset. Additionally, it fixes issue #555 regarding the Thielen et al. 2021 dataset, and issue #554 that fixes a bug and makes datasets in the c-VEP paradigm searchable.

[PierreGtch]

Fixes #554 Fixes #555

[PierreGtch]

@thijor Thielen2015 and Thielen2021 share multiple methods copy/pasted methods. I think it would make sense to define them both in the same thielen.py file with a common parent class to facilitate maintenance in the future. Lee2019 for example does this

[thijor]

@thijor Thielen2015 and Thielen2021 share multiple methods copy/pasted methods. I think it would make sense to define them both in the same thielen.py file with a common parent class to facilitate maintenance in the future. Lee2019 for example does this

You are right, Pierre. However, also the castillos2023 dataset uses these functions, as these are the ones that embed epoch and trial information in the datasets as separate stim channels. So a general thielen.py is not handy. Would be more like utils. Where would you want to put it then?

[PierreGtch]

@thijor Thielen2015 and Thielen2021 share multiple methods copy/pasted methods. I think it would make sense to define them both in the same thielen.py file with a common parent class to facilitate maintenance in the future. Lee2019 for example does this

You are right, Pierre. However, also the castillos2023 dataset uses these functions, as these are the ones that embed epoch and trial information in the datasets as separate stim channels. So a general thielen.py is not handy. Would be more like utils. Where would you want to put it then?

Then I think these functions would fit in moabb/datasets/utils.py