#106 Add cell explorer new files

I added new files for the CellExplorer format, they are stubbed spikes files in both the classical format of matlab and the new hdf5 supported ones.

Hi @h-mayorquin! Can you push your feature branch directly to the Neuralensemble/ephy_testing_data repository? Otherwise git-annexed content will be unavailable after merging as annexed files are not duplicated upon merge. I added you as a collaborator, so you should have the right to push directly to this repo.

What a strange behavior.

I opened another PR then: https://gin.g-node.org/NeuralEnsemble/ephy_testing_data/pulls/107

Feel free to close this.