Add sonar-runner support to Gradle and Powermatcher

Gradle sonar-runner support had some issues: out-of-memory, crashes, etc. A stand-alone sonar-runner works like expected.

Since Powermatcher is a multi-module project, some additional configuraiton is needed to get sonar-runner working correctly. Mainly specifying where the modules and libraries are located. 
Based on this example: http://paulonjava.blogspot.nl/2013/11/building-bndtools-projects-with-gradle.html, I created a task within the main build.gradle file to generate a sonar-runner.properties file in the root of the workspace.

This file can then be used in for example a separate sonar-runner or jenkins to perform a sonar analysis. I have not added any database of project information, since this is up to the user and keeps the file reusable.

To perform a clean build and output sonar settings with gradle: 
<blockquote>gradle clean build generatesonar</blockquote>