Align package structure among all benchmark implementations

The package structure in each Gradle project should be as follow:

• rocks.theodolite.benchmarks.<uc1-4>.<kstreams|flink|beam|beam.flink|beam.samza|hazelcastjet|commons>
• rocks.theodolite.benchmarks.commons.<kstreams|flink|beam|beam.flink|beam.samza|hazelcastjet>
• rocks.theodolite.benchmarks.loadgenerator

With changing these packages, we might also need to do some refactoring in Dockerfiles, Docker Compose files and Kubernetes resource files (whenever we refer to classes by their name).