Refactored all entity classes: added an interface for each entity, such that alternative data stores can swap out the entity objects with more fitting ones (eg with annotations like Neo4j, JPA, etc or other mechanisms. Internally, only the entity interface is used)

# By sasdbm
# Via Joram Barrez (2) and sasdbm (1)
* 'activiti6' of https://github.com/Activiti/Activiti:
  Remove duplicate semi-colon
  Fix string concatenation when used as argument of append() call

Fix string concatenation when used as argument of append() call

Remove duplicate semi-colon

Fix for failing Oracle QA

# By sasdbm
# Via Tijs Rademakers (1) and sasdbm (1)
* 'activiti6' of https://github.com/Activiti/Activiti:
  Remove unused imports in engine project

Refactoring the persistence: splitting of persistence specific code in the EntityManager classes into a DataManager class.
The EntityManager -> EntityManagerImpl  now each have a dedicated DataManagerImpl that contains all the MyBatis specific code,
effectively making it possible to plug that layer with some other implementation.

Note: Still need to check the usages of DbSqlSession in the behaviors/commands, but those should be easily portable too.

Remove unused imports in engine project

# By Tijs Rademakers (4) and sasdbm (1)
# Via Tijs Rademakers
* 'activiti6' of https://github.com/Activiti/Activiti:
  Manual merge of pull request 656
  Move to Activiti 6 beta 2 snapshot version
  Release notes + migration docs changed for Activiti 6 Beta 1 release
  Move to 6.0.0.Beta1 version
  Fix string concatenation when used as argument of append() call

Fix string concatenation when used as argument of append() call

Disable javadoc generation on -Pcheck (+2 mins extra!) and fix build script to add java8 profile when building on jdk 8

Making entity manager interfaces consistent: removing duplicate methods (findById/getEntity/..) and make sure they pass the entity cache

Refactoring entity manager usage: making the entity manager instances engine-scoped instead of a Session implementation (ie command scoped).
This way, all the previous Context.getXXX calls can be replaced by direct invocations. Won't influence performance that much, but still nicer from an architectural point of view.

Refactoring EventSubscriptionEntityManagerImpl: use the getList that goes to the cache instead of use a local list (needed to make entityManager classes engine scoped, instead of command scoped.

# By Tijs Rademakers
# Via Tijs Rademakers
* 'activiti6' of https://github.com/Activiti/Activiti:
  Refactoring for Activiti 5 compatibility + Spring, CXF and Camel unit testing