Added a virtual destructor to the Server ABC. Cannot forget that!
World.h now includes what it was missing.

The only reason it was compiling without error was the needed headers
were being included before World.h in particular.
Added a find-by-id function for the World class.

It's a non member function which just wraps a regular std::find_if call.
There is now a Local Server implementation.

It is non standard. Stay tuned.
The non-standard functions in LocalServer are now part of the ABC.

By implementing them locally and concretely first, we know it's easy to
implement and not kind of clunky. Sort of a live test of the interface.
All of the client code now uses regular ints instead of 16 bit ints.
There is now a function in the Server ABC which should return every paddle.

It is implemented in the LocalServer.
Label is now slightly towards the buttons. 35 pixels down.
ppmclient is now linked to ppmserv.

Can't say why it wasn't before, but it is now.
Added a "paddle creation game state" for testing.

It is currently disguised as singleplayer mode.