Enable support for SonarQube 4.2

The problem was that `sonar-pitest` would use the `3.7` API, and when running on `4.2`, the following error message would be received:

```
Not supported since v4.2. See http://docs.codehaus.org/display/SONAR/API+Changes
```

Basically, `org.sonar.api.resources.JavaFile` were deprecated.

Also, I guess, http://docs.sonarqube.org/display/SONAR/Plugin+version+matrix should be updated.
With the `JavaFile` gone, we require to pass in the actual path to the `context.getResource()` call (via a `org.sonar.api.resources.File` instance).

To find that path, I just look up the corresponding `.java` file  from the file system (see below)