Add standard example framework

[oubiwann]

To date, most of this work has been tracked here so far:

• Task: Port Mesos Java Example to Mesomatic mesomatic#10

Dev plan:

• Create test-framework.clj as a port of TestFramework.java
  • Implement basic callbacks
  • Track tasks finished count
  • Check for total == finished, and stop driver in that event
  • Add checks for TASK_LOST, TASK_KILLED, and TASK_FAILED (as well as driver abort, when applicable)
  • Check for implicit acknowledgements, and send status if not
  • WONTDO - Add ENV variable checks (skipping this ... no real educational value in it; PRs welcome for those who think it should be here, though!)
  • Find out where to do DRIVER_STOPPED checks and make a stop call in that event
• Create test-executor.clj as a port of TestExecutor.java
  • Implement basic callbacks
  • create new task status and set state to TASK_RUNNING
  • send status update to executor driver
  • log message about "Running task"
  • create a new task status and set state to TASK_FINISHED
  • wrap in try/catch
  • run the whole thing in a new thread
• Create core.clj with main function
• Add lein alias(es) in project.clj for running framework and/or executor
• Create tickets and submit PRs for all bug fixes/feature additions
• Test all Mesomatic bug fixes/feature additions in a separate (cumulative) branch
• Demonstrate the ability to send messages from the executor back to the scheduler
• Ensure proper shutdown of framework upon successful completion of tasks
• Perform a final compare & contrast between Java and Clojure versions to ensure implementation parity