fix(subprocess): Add handling for collapsed and expanded subprocess.

- DI for a new subprocess has attribute "isExpanded=true", for that it is
  necessary to override the method "createDi"
- default value of attribute "isExpanded" is "false"
- change handling of "BPMNDIAttributeDefault.USE_DI_VALUE" to get the
  DI value of the current BPMNShape for subprocesses
- change super class of "ExpandFlowNodeFeature" because it seems that the
  old super class "ShowDiagramPageFeature" make no sense in the subprocess
  context

related to #CAM-1500