ACT-2063 extended diagram wizard still uses Activiti constants

Related to ACT-2023

The CreateDefaultActivitiProjectWizard setWIndowTitle() method had
hard-coded Activiti constant.

Missed a method that requires updated visibility (private to protected)
to rebrand/repackage. The CreateDefaultActivitiDiagramWizard method
getDiagramName() should be protected. The 

Found while testing recent resolved issue ACT-1964.

Change Id: b1ef92ecb402e872167e6927f9d4bcdcce0761a6