Implemented basic input function and tested for the three test cases

I used a list of lists because JSON does not have a concept of tuples. Look here http://json.org/ 
If we really want a list of tuples, then we can convert the lists to tuples by iterating through the dictionary returned by inputNetwork, but I don't think it is worth the effort because the dictionary will be used only once to setup the host, link, flow and router objects.