Maven support

I have refined both drupal-computing and drupal-recommender to execute the recommender program in maven way. Here are the steps.

At drupal-computing
- mvn install -DskipTests 
This will install the computing-core-7.x-2.0-alpha2.jar into local maven repository. This file is required by drupal-recommender, and have been added a dependency in pom.xml.

At drupal-recommender
- mvn exec:java 
The folder need to have config.properties in order to run the recommender program.