Fix Sesame's transaction handling

I reconsider a bit my attitude. I agree that Sesame.begin() and Sesame.commit() is useless in remove() operation. Update operation is more complex and therefore I think this is the correct way. Update consists of two operations : add and remove. It has to be in transaction either Sesame's or RDFBeanTransaction. If add() will fail we have to ensure also remove() operation will be rollbacked. At the same time, it will improve performance as the will be send to repository at once and executed together.