Start using JCov for code coverage

Since we might face problems running e.g. the uitests in future build and test systems, we need a way to measure how much of the code is actually tested. We used to have JaCoCo for this, but JCov is probably a better choice since it is supported in house (=will work with future versions of Java earlier). We also believe it is easier to use JCov if others do that with Mach5 etc.