chore(tree): Add testcase for tree directive

- add some testcase to test the directive tree

related to CAM-719
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
chore(db2-upgrade): fix comments in DB2 upgrade script
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
fix(db-upgrade): upgrade script for oracle

related to #CAM-897
fix(db-upgrade): use simple script for db2 & mysql

- on mysql & db2 we do not perform full migration but provide a good
  enough approx.

related to #CAM-897
chore(diagram/tree): add additional testcases

- add further testcases to test the selection of a bpmn element or a node

related to CAM-719
chore(test): Add tests for activityInstanceService

- add some test cases to test the behavior of the activity instance
  service
- add documentation to activity instance service

related to CAM-719
chore(test): Add tests for activityInstanceService

- add some test cases to test the behavior of the activity instance
  service
- add documentation to activity instance service

related to CAM-719
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
Merge branch 'master' of github.com:camunda/camunda-bpm-platform