Implement a proper log system

[Conr86]

At the moment, there is no logging system other than printing to the console.

We need a proper log system, I've been looking at loguru which looks excellent. We just need to sort out how to do it between processes. I think either sending the pickled log data or just the final log string over the process pipe should be fine.

[Conr86]

The logging branch contains an overhaul of the logging system. We're now using Python's built-in logging system and logging to stdout, not to a file. This is intentional, as supervisord will capture the log from stdout and save it to a file, as well as making it available on the web interface. This means we can have the log displayed on the SARTInterface (under the log modal). supervisord also provides a XML-RPC API to start / stop processes, and get the contents of the log, among other things.