Add c-VEP paradigm and first dataset

[thijor]

Closes #366

[PierreGtch]

• update whats_new
• add your name to list of contributors (bottom of whats_new)
• update the list of datasets in the doc
• update the list of paradigms in the doc
• update the datasets_summary file in the doc
• add tests for the cVEP paradigms in tests/paradigms.py
• add cVEP case in tests/benchmark.py, in test_benchmark_strdataset() and test_benchmark_objdataset()
• test also, with a fake dataset, the case when there are more than two stimulation levels

[bruAristimunha]

Hi @thijor and @PierreGtch!

The code is very good! I was reviewing, and I posted my main comment in the review. It would be lovely to try to create some function in the thielen2021, especially in the part get_single_subject_data, to allow and to facilitate the integration of new CVEP datasets :)

[bruAristimunha]

I will fix the pytest issue

[bruAristimunha]

I am happy :)

[PierreGtch]

Me too :D

[bruAristimunha]

Thank you @PierreGtch and @thijor =)

[bruAristimunha]

Online @thijor and @PierreGtch
https://neurotechx.github.io/moabb/dataset_summary.html#c-vep
https://neurotechx.github.io/moabb/generated/moabb.datasets.Thielen2021.html#moabb.datasets.Thielen2021

To use, please install from the github until next release:

https://neurotechx.github.io/moabb/install/install_source.html#installing-moabb-from-the-source