PROBABLY WON'T FIX:
Embedded rules language not updated when language is set (in Analyse, Game and Problems)
If new live game starts in background, "new game" notify OK but not first move.

"FreeBoard", re-using a lot of Board logic, but with SVG (empty) board + SVG (empty) reserves.
Will be used for variants with custom non-rectangular board (Hex, at least)
Or, with other board shapes (see greenchess.net for example)