Logging strategy and configuration

[ivansenic]

Let's copy the old logging strategy we had with log-back originally in inspectIT.

But:

• keep the log-back config in the classpath resources so it's used by default if the external file is not found
• include the log-back configuration to the released artifact next to the inspectit-agent.jar (as now, but this time only use this as a reference for the user)
• ensure that property exists that can point to some other location configuration file
• remove the MinLog that we used originally because of Kryo

Maybe we should provide some easy logging config in the configuration file. This way a user can easily configure logging as everything else.