Support different kinds of queues through a trait.

[elshize]

Breaking change

Instead of add_queue and add_bounded_queue, there is only add_queue that takes the queue as argument. This allows for cleaner API and different queue support:

simulation.add_queue(Fifo::default());
simulation.add_queue(PriorityQueue::bounded(5));

Type inference should work most of the time, which cleans up the code. In case it's not possible, one can instantiate a queue explicitly:

Fifo::<i32>::default()