refactor/test: test and improve BpmnTransformer, BarTransformerTest

create new test process file which contains manifest tag
BpmnTransformer is now thread safe because his fields are now final
switch BpmnTransformer from static to instance methods
remove unused method in BpmnTransformer
remove @Ignore from BarTransformerTest
BpmnTransformer now creates ZipEntry for directory stated in
"Process-Defintions" if that's present in BPMN-file