Display which config is used in --more_version

In the output of i3 --moreversion,
display the path of the used config and its last modified time.

src/ipc.c

@@ -814,6 +814,9 @@ IPC_HANDLER(get_version) {
     ystr("human_readable");
     ystr(i3_version);
 
+    ystr("loaded_config_file_name");
+    ystr(current_configpath);
+
     y(map_close);
 
     const unsigned char *payload;