Add support for depends(field), identifier and clientIdProperty(model).
Add ModelId, ModelCleintId and ModelVersion annotations as an
alternative to the correspondig configuration on Model

ralscha/extclassgenerator#12
ralscha/extclassgenerator#13
ralscha/extclassgenerator#14
Compile with Java 8 because of the @Repeatable annotation
Introduce new field annotations as alternative to Model.idProperty,
Model.versionProperty and Model.clientIdProperty

ralscha/extclassgenerator#15