support open ephys datasets

[d1manson]

This won't be super-easy to do, but with a little bit of work in the file-organiser and some basic copy-paste-modify of a few functions in parsed-data it may not be too tricky.

Oh, except we suddenly do need to care about sampling rates, where previously we have been able to ignore the possibility of bugs due to mismatched timebases.

I guess there's also the question of continuous recordings..I'm not sure at what point detected spikes are separated from the rest of the data.