Change payment logic

[jorgeramirez]

Since we have added a minimum number of tasks parameter to the Job, we need now to change the payment logic. When need to implement a method that for a given job will compute the HIT reward. This method should take into account #number of quizzes, #minTasksParameter, honeypots frequency. So when publishing a HIT, we will add as the reward the value computed by this new method.

The sendBonus method of the JobManager will change so that the value of the bonus should be the total reward of the worker minus the number computed by the new method (HIT reward)