Set logLevel on WayangContext to allow doing it without conf file

[juripetersen]

This proposes a functional interface to change the Loggers level with the WayangContext:

context.setLogLevel(Level.ERROR);

The change provides better ergonomics and prevents having to fiddle with configuration files, when Context objects etc. can be created during plan building. Furthermore, this aligns with the API presented in other Apache projects like Spark