signalGiver/Receiver update .giver/receiver variable only before sending the signal to the receiver/giver

Exit object has its own haveToDispose which always returns False. Other minor corrections to Machines and OperatedPoolBroker

new methods that block the entry of an object. Implemented on machines to avoid receiving to signals at the same simulation time

Machine now communicates with Broker via events. Machine waits for isRequested signal to getEntity. Can also get an entity after a loadOperatorAvailable event in case it could not getEntity due to resources lack

new CoreObject method initialSignalReceiver. Invoked as the generator of the objects starts and control if there is WIP assigned to them and signals receivers

ObjectInterruption interrupts or signals the victim according to the state of the victim (waitToDispose)