instantiates an object from class of createDiversion
createDiversion(name,label,downstream,divertTo,capacity)
a string: the name of diversion to be instantiated
an integer: the code of downstream object
an integer: a unique number, as label
an integer: the code of an object at the diversion outlet
diversion capacity (cms)
a list: an object from class of list instantiated by createDiversion