StageConfig.setReadOnly(), .setNonTransactional() (as well as set[Non]Idempotent(), .setSafe())

[stolsvik]

Related to #49, where the stage lambda can runtime mark the processing as idempotent etc, it might give room for more optimizations if the entire stage was marked.

1. If it was ReadOnly, the SQL transaction (and connection?) could be marked as such (ref Spring)
2. If NonTransactional, neither JMS nor the SQL Connection would be transactional, resulting in speed boost.