Chess (Multiplayer)

[Gerold55]

Request to add multiplayer.

[bell07]

Currently mutliplayer is possible if both player look to the the same laptop / computer.

Network multiplayer require to synchronize the used chess-table "inventory" in any way.
This question was asked already in #119

The chess implementation is based on minetest-mods/realchess that is based on xdecor version. The laptop version needs to be updated to the last changes in both other mods bevor any enhancements. See minetest-mods/xdecor@ee7a281 for example that is useful for laptop anyway.