Cleaned up the paddle management.
Tests no longer fail to compile, but they fail to link.
Removed a lot of server code.

Disabled ppmserv, ppmclient and ppm.
Documented a paddle endpoint, finally in the struct itself.
Added a 'connect' function to the server interface.
There is now a mechanism to store the various things one might find on the screen.
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.