launch_daemon: added support for arbitrary ports.

* Dropped "create_port" -- this is now the default for services.
* Additionally (or alternatively, if you use the "legacy" mode), you can
  now create named ports, and specify their capacity.
* Added convenience methods to BLaunchRoster that automatically use the
  signature of the current be_app.

src/kits/app/Application.cpp

@@ -531,7 +531,7 @@ DBG(OUT("BApplication::InitData() done\n"));
 port_id
 BApplication::_GetPort(const char* signature)
 {
-	return BLaunchRoster().GetPort(signature);
+	return BLaunchRoster().GetPort(signature, NULL);
 }