Shared gradle

For all the flexiblepower projects, we are now switching to gradle. This also means that the shared configuration is now suited for gradle. I suggest that all the projects switch to this.

This already adds a couple of plugins (e.g. for code coverage, checking of code style and generation of javadoc) and implements a distribute task. You can look at the current distribution at http://fpai-ci.sensorlab.tno.nl/builds/powermatcher/shared-gradle/LATEST/