implement vendor specific update systems

[s4ke]

For EclipseLink we can use SessionEventAdapters (for Transaction callbacks) and DescriptorEvents (for change events).

For Hibernate we can just use the same system Hibernate Search ORM has.

[s4ke]

OpenJPA has such a system as well.

[s4ke]

we need to implement UpdateConsumer logic for these as well.

[s4ke]

tests for flush only (no transaction active) have to be implemented as well.

[s4ke]

we need to test this in a JTA environment as well.