Read frame data

This MR adds functionality to read in data from a frame. It requires the frame file to be specified along with a few other arguments.

It has a very primitive attempt at guessing the channel name if it isn't specified.

I haven't written up an example yet. I can probably do this, although it requires having a frame file.

Have I missed anything important for reading frames @eric.thrane @rory-smith @sylvia.biscoveanu?

@gregory.ashton I duplicated some of your data processing for the open data to utils, do you think we can rewrite it in this way? Is it possible to use either the frame of h5 file provided in LOSC, I think that would allow the same logic to work for open data examples.