Log-to-site packet

[Xyene]

Sometimes it'd be useful for the judge to be able to send some log packets to the site, where they can be logged through Django's logger. This would enable certain messages to be filtered and logged to more visible places (e.g., Slack).

For example, if a judge fails to initialize a runtime, this should be reported to somewhere an admin can see, even if it's not a fatal error.