Support for TextAnnotation and MultiInstanceLoopCharacteristics

* Added ```TextAnnotation``` interface and ```TextAnnotationImpl``` class and related interfaces and classes in order to support BPMN 2.0 TextAnnotation element
* Added ```MultiInstanceLoopCharacteristics``` interface and ```MultiInstanceLoopCharacteristicsImpl``` class and related interfaces and classes in order to support BPMN 2.0 MultiInstanceLoopCharacteristics element