Enable system evolution before first nucleation event

[david-montiel-t]

Currently, the code does not allow the system to evolve before the first nucleation event occurs.

We want to have an option in parameters.in that lets the user specify whether to alloy evolution before the first nucleation event and and modify the following section of nucleation.cc (lines 29-47) in the core library accordingly:

        if (currentIncrement == 1){
            while (new_nuclei.size() == 0){
                currentTime+=userInputs.dtValue*(double)userInputs.steps_between_nucleation_attempts;
                currentIncrement+=userInputs.steps_between_nucleation_attempts;

                while (userInputs.outputTimeStepList.size() > 0 && userInputs.outputTimeStepList[currentOutput] < currentIncrement){
                    currentOutput++;
                }

                while (userInputs.checkpointTimeStepList.size() > 0 && userInputs.checkpointTimeStepList[currentCheckpoint] < currentIncrement){
                    currentCheckpoint++;
                }

                new_nuclei = getNewNuclei();
            }
        }
        else {
            new_nuclei = getNewNuclei();
        }