Added util package: MultiMap implementations (HashMap based and HashMap
based supporting biased sampling from an image).

Added new Node method: getOutputLinks(), to facilitate building network
topological structure.

Added Switch class: Exceptions upon getting a message destined for it,
does nothing on update, uses deferred scheduling.

Redesigned Schedulers:
-Main scheduler class, uses scheduler-reserved fields in
DeferredSchedulingNode to perform book-keeping out of the eyes of a
Node.
-FIFOScheduler: Scheduler that implements FIFO
-VOQScheduler: Scheduler that facilitates VOQ scheduling strategies;
must extend to implement createProgram, which returns the set of edges
to actually schedule at a node.