Allow injecting logger or logger factory

[xerial]

Currently Airframe uses the default logger (airframe-log). It might be useful if we can inject loggers (e.g., slf4j, scribe, etc.).

[xerial]

Injecting some LoggerFactory will be OK, but addtionally we need to pass the current class information to build a logger instance:

private val logger = {(cl : ThisClass, l:LoggerFactory) => LoggerFactory.of(cl) }