Added shutdown() and systemsShutdown() to headers

shutdown() is a virtual function, so no need for anything more there.
systemsShutdown() is the same as systemsUpdate(), so just need to dupe it.
Added systemsShutdown()

Just a basic copy of systemsUpdate()
Updated test program Systems to fit new format.

Due to changes in the CLD-ECS Framework, the Systems in ECS-Test had to be
tweaked appropriately. The program now compiles and runs, but there's a
memory leak when the program completes. :(
Updated System and World with new way to connect Library to System

Got rid of the old way of passing a Library through the init() function of a System; it's now
done as the System is added to the list of systems in World via linkLibrary().

shutdown() was also added to Systems and systemsShutdown() to World.