Visualize StreamGraph and ExecutionPlan

Based on SAMZA-1178, we are able to generate the JSON representation of StreamGraph and ExecutionPlan. We need to provide a visualizer to render the json as DAG and let users to view it.

First look: https://xinyuiscool.github.io/visualizer/plan.html. This is based on the example graph JSON generated in TestJobGraphJsonGenerator.

For the api-test job:

For the join-test job:

How to visualize the plan (locally):
Once a Samza application (using fluent API) is deployed, an execution plan will be generated by the ExecutionPlanner. The plan JSON will be written to a file (plan.json) under the bin directory, which also contains the plan.html and javscripts (js folder). So the bin dir has the following for visualization:
./bin

• plan.json
• plan.html
• /js
• d3.js
• dagre.js
• planToDagre.js

Then deployed locally, the user can directly view the plan by enter the following in a browser:
**file:///my/samza/app/dir/bin/plan.html**

To visualize the plan remotely, the user can either scp the files into local box and view the plan there, or bring up a simple http server to serve the page.

In the future when we have the Samza dashboard, we can add the plan visualization there to avoid the above manual steps.