GUI improvements - look and operation.

Improved the appearance of embedded widgets in the tables (push buttons and wifi signal bar).

If there is only one WiFi service that can be operated on by pressing either the "connect" or "disconnect" buttons it is no longer necessary to select that service before pressing the buttons. The service will be selected automatically.

Single instance code revised to use sockets instead of shared memory. If another instance of the program is running and a second instance it started the first will be raised, the second will abort, and a message will be printed to stderr.