Use SocketAppender and slf4j as logging api

- Deprecates com.findwise.hydra.Logger (simply use slf4j instead)
- Uses SocketAppender in the stages and SimpleSocketServer in the core
- Removes InternalLogger class. Use LoggerFactory.getLogger("internal") instead.
Various fixes and improvements to the new Logging API.

Also makes sure that ConsoleAppender can be turned on again if the situation requires it.
Adds logging config to properties file.
Merge pull request #197 from laserval/socketappender-merge

Replaces logging with slf4j and SocketAppenders