UI: save and load table/tournament settings to file

New table/tournament dialog must have button to save and load game settings. It's already have "load last configuration" buttons but it's a different approach.

TODO:
* [ ] make game settings config format (as example: json);
* [ ] file format must be compatible between table/tournament modes (e.g. you can load table config for tournament dialog and setup missing values);
* [ ] configs can contains small number of settings or other data (as example: image name and description for server side competitive/event);
* [ ] add buttons to save and load configs (table + tournament dialogs);
* [ ] add sample folder with standard configs for popular game and modes (see sample deck example).

P.S. #446

Start by locating the new table and tournament dialogs and the existing "load last configuration" buttons. Review the sample deck example for the proposed sample-config folder, then determine how shared settings and mode-specific values should be represented. Done means both dialogs can save and load compatible configurations, including optional settings and sample configurations.

Written by the indexing model from the issue text.