Command line hook and logging for splash.

[davidorme]

splash_v1 was written as a command line application and providing a entry point through pyrealm to allow it to be used in that way again would be good.

As part of that, we'd likely want some kind of logging process to report on activity and the feature/splash_v1 branch includes a logger.py module that was used to do this in the previous implementation. Something needs to be done with that logger.py functionality. We could just strip it all out (and still have an entry point) but it seems more sensible to integrate it and retain the logging.

At the moment, pyrealm doesn't emit logging messages for anything. That's based on the idea that it is primarily used interactively via notebooks and scripts rather than running command line applications, but I think that is likely to change. I'm not sure whether we initially just roll out logging for SPLASH and then think about what other entry points we might want to add and which might then need some logging messages added.