Model compiler should not duplicate files across runs

If you don't mvn clean each time you generate the executable model, new files will be generated at each run.

These seem to be the culprit:

PackageModel#getPackageUUID

    private String generateRulesFileName() {

        return RULES_FILE_NAME + generateUUID();

    }

solution: use a counter; the compiler is single-threaded, two runs produce the same output, existing files will be just overwritten

deliverable: test case verifying files do not grow in number across runs