[WIP] add Activiti 5.19.0.2, 5.20.0 and jbpm 6.4.0

[matthiasgeiger]

• [X] create class for activiti 5.20.0
• [x] add to repository
• [x] update default versions activiti and camunda
• [x] upload files to SVN (activiti-5.20.0.zip + groovy-all-2.4.5.jar)
• [x] the same for activiti 5.19.0.2 :wink:
• [x] the same for jbpm 6.4.0 :wink:
• [x] add system tests

[simonharrer]

Could you add the engine to the tests in travis?