Consolidate how we do logging in plugins

[ktoso]

The plugins are very messy in how they log, don't really have log levels and have different styles.

It also can be very useful to know where we log and if we're in a command plugin or swift-java in Swift or in Java or some other invocation since things get complex quickly.

Currently this is manually done through a mix of printlns and wannabe logging.

We should probably just adopt swift-log and also make a simple logger type for the Java side of the libary that logs in the same style.