Fixes for network calculation issues
This fixes several issues:
* More than one switching station could become active on large networks
 - Switching stations now semi-permanently become disabled if another is present
 - Power monitors have been added to replace the function of "slave" switching stations, to discourage overuse of switching stations
* Networks did not reliably "split" when cutting a cable
 - I "may" have caused this issue, but I believe it is solved by this
* Machines did not run without a player near the switching station
 - Active switching stations now forceload themselves, and free the forceloaded block if disabled, dug, or disconnected
 - Machines are only loaded to run them (as before), so only one mapblock (or two if the bottom edge of the switching station is a mapblock boundary) is loaded
 - Cables are still only loaded during a full network recalculation