This adds a number of gravitational wave utils functions which are used by scripts in bilby_pipe. For now, I don't intend to expose these to the bilby user interface (though they are of course accessible via the utils).
The function load_data_from_cache_file was originally written by @colm.talbot in bilby_pipe, I'm moving it here as I can think of this as more of bilby operation than a bilby_pipe operation. This may also have some overlap with bilby.gw.utils.read_frame_file, @colm.talbot what do you think?
