Need a way to "just load a g3 file from a book"

[Katie Harrington]

I suspect this will be an important debugging tool and that detector folks / lower level folks will want it.

I have confirmed that sotodlib.io.load_smurf.load_file will not work for this as-is because we have renamed data --> signal and (the harder fix) the loader works out all the resonator name keys. It expects the names of the detector signals to be in the "r000" format but we have re-named them all to readout ID.

I think we should split out the functionality in load_book or something there instead of patching the load_file function. This is because that should also be loading the ancillary data as well.

[Matthew Hasselfield]

Addressed in #526