Configure JPA persistence for data models

Improve data modeler to provide at least a basic configuration for JPA persistant entities, and make/test all modifications to engines to make sure they are supported for non-global classes (not in the global classloader)

This should already be possible, using pluggable variable persistence, and we have an implementation for JPA entities already. That means that the engine will not save the entity as part of the process instance state but save / load it from separate entity tables. We might >have to look at extending the configuration options (to persist using a different data source for example).

This feature is not in 6.0.