fix: update how debug logging works

[nicklasl]

Only logged invocation coming from the SDK that matches the logging level defined by the customer will be printed to Logcat.

The idea here is to have the customer supply the lowest level that they want to get logs for -- they would do that in the create function where we now default to LoggingLevel.WARN.

The SDK is then opinionated about which level to log different things on, for example:

    override fun logEvent(action: String, event: EngineEvent) {
        debug("[$action] $event")
    }
    // and
    override fun logContext(context: Map<String, ConfidenceValue>) {
        verbose(context.toString())
    }

Warnings and errors can contain message from a throwable.

[nicklasl]

Note to self: Don't forget to also update the Readme docs.