Multi instance refactoring: introduced the 'IS_MI_ROOT_' column to indicate an execution is the root of a multi instance. Every multi instance (sequential and parallel, parallel already had it) will now spawn an execution that acts as parent for the whole multi instance. This has two benefits: cleanup becomes way easier and it opens up the possibility to dynamically add new instances to a multi instance (not yet implemented).

Porting 'terminateAll' to v6: cherry pick of https://github.com/Activiti/Activiti/commit/a67374d65b93b22590da9e45e149e5433c35408e

Porting 'terminateAll' to v6: cherry pick of https://github.com/Activiti/Activiti/commit/0727dd10c86cbb50089979289e300c6998a159b2

# By Tijs Rademakers
# Via Tijs Rademakers
* 'activiti6' of https://github.com/Activiti/Activiti:
  #710 PR merge to Activiti 6
  Fix history level checking in test
  Fix Activiti 5 compatibility issue due to wrong Context class
  Added dyanmic bpmn support for sequence flow conditions and scripts

Fix activiti 6 UI not working on some languages (see https://forums.activiti.org/content/activiti-6-ui-internationalisation-problem)

Implement ClassDelegateFactory and DefaultClassDelegateFactory, and use them in the DefaultActivityBehaviorFactory and the DefaultListenerFactory.

Added accessor methods to ProcessDefinitionQueryImpl and DeploymentQueryImpl.

ACT-4079 (NullPointerException in DbSqlSessionFactory.isBulkInsertable() when Custom Entity is inserted) : fixing Oracle, the old 'get()' needs to be back, but now _after_ the containsKey

Activiti6 Modify ClassDelegate to so that the way it instantiates classes can be overridden.

Rename ClassDelegate.instantiateDelegate to ClassDelegate.defaultInstantiateDelegate for external class, and added a non-static method for internal calls.