Add logLevel property to enable different log levels for the examples. Motivation:
When running the examples using the provided run-examples.sh script the log level is 'info' level. It can be handy to be able to configure a different level, for example 'debug', while learning and trying out the the examples.
Added a dependency to logback-classic to the examples pom.xml, and also added a logback configuration file. The log level can be configured by setting the 'logLevel' system property, and if that property is not set the default will be 'info' level. The run-examples.sh was updated to show an example of using the system property to set the log level to 'debug'
It is now possible to turn on debug logging by settnig a system property on the command line.