To have a pom.xml in the root folder to assemble these submodules together

[breakdawn]

There are several submodules in this project, it would be convenient to manage the code if there's a pom.xml in the root folder to wrap them together. This will also help get rid of 'install' while developing. Here's an example from Apache spark: https://github.com/apache/spark/blob/master/pom.xml