feat(engine): rename all activiti.cfg.xml to camunda.cfg.xml
- add compatibility mode for activiti.cfg.xml
- activiti.cfg.xml in engine-cdi is the testcase for the usage of
  activiti.cfg.xml

related to CAM-972
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
fix(engine): temp disable DURATION on db2

related to #CAM-1097
Merge branch 'master' of github.com:camunda/camunda-bpm-platform