Add chess engine support to build mode

[GoodChessMind]

Have newest stockfish engine available on your website.

If possible with the UCI engine allow to play against engine mode to create openings.

Also, if possible allow UCI engine to pick random moves in openings (not necessarily the best move the engine has calculated)

[jven]

More user feedback: "WOuld it be possible to have engine support while building the repertoire and a library of Grand Master games !"