WIP: enhanced paging

src/main/java/org/caosdb/server/entity/Entity.java

...org/caosdb/server/entity/xml/ParentToElementStrategy.java

src/main/java/org/caosdb/server/jobs/TransactionStage.java

src/main/java/org/caosdb/server/jobs/core/ExecuteQuery.java

src/main/java/org/caosdb/server/jobs/core/Paging.java

...main/java/org/caosdb/server/jobs/core/RetrieveAllJob.java

src/main/java/org/caosdb/server/query/Query.java

src/main/java/org/caosdb/server/transaction/Retrieve.java

src/main/java/org/caosdb/server/transaction/Transaction.java