Add missing dependency to the beacon library.

Adds the 'forwarable' module back to the beacon board library,
which fixers a dependency issue when the libraries were called
in a non-standard order.
Change to sparse serial transmission.

-Adjusts serial transmission to occur one time per second,
 rather than as fast as possible. This encourages the contestants
 to use the bright lights atop the beacon to locate each beacon,
 rather than a constant stream of IR.
-Beacons now transmit a new pseudo-random code every second,
 rather than the same code repeatedly.
-Contestants now have only one second to respond to a beacon's
 query. This ensures that contestants have to "sync up" with the
 beacon.
-The anti-spam behavior is changed: if they beacon receives an
 incorrect code, it will stop listening for a full minute.
 This should probably be accompanied by a visual indication,
 in future versions.