Redesign with load generators as strategies

1. Each different load generator now is a LoadGenerationStrategyI. Instantiation uses a simple factory that takes the config file and unmarshals it into the necessary load generator.
2. Added command-line options for specifying the type of load to be generated.
3. Load generation config files are written in YAML format.
4. Using Gradle as the build tool.
5. Dockerfile updated to now build single image for system-load-generator.
6. Image pkaushi1/system-load-generator:v2 created and pushed to docker hub.