Handle "show touches" on the device-side

Now that the server can access the Android settings and clean up
properly, handle the "show touches" option from the server.

The initial state is now correctly restored, even on device
disconnection.

app/src/server.c

@@ -268,6 +268,7 @@ execute_server(struct server *server, const struct server_params *params) {
         "true", // always send frame meta (packet boundaries + timestamp)
         params->control ? "true" : "false",
         display_id_string,
+        params->show_touches ? "true" : "false",
     };
 #ifdef SERVER_DEBUGGER
     LOGI("Server debugger waiting for a client on device port "