TODO: the GUI will have to make it a float too

Notes:
  * Input format changed (Source.part now is a full name)
  * __init__ must handle complex data structures for processingTime & interarrivalTime instead of having flat parameters
  * type conversion must be performed ("1" != 1), probably we can assume json has correct type and have the gui produce proper json

bug in Machine canAcceptAndIsRequested fixed. Now exit is assigned in every occassion that true is returned