Location Server Running

Location server tracks the status of up to 2 trains,
although I've only tested one. Distance past sensor
isn't monitored yet. User prompt listens to the
location server and prints the locations of trains.

Moved some helper methods for dealing with track nodes
from dijkstra.c to track_node.c

Added a queue_iterator, even though I never ended up using
it.

Increased the stack size to 64KB.