Singleplayer update

Creating brand-new singleplayer mode.
Many fixes and memory optimisation.

More fixes

Some small fixes.
Fix placing number near board.

Fixed castling and pawn transform

Better UI

Adding some UI indicators near game field

Multiplayer fixes

Fixing most issues with game modes (mostly with multiplayer).

Multiplayer

Adding (near working) multiplayer mode (LAN mode) to connect on different computers to play.

Working game

Now fully workable chess for two players (with some small issues)

First test of new engine

First normally working prototype of new game engine, based on OOP and SOLID with multithreading.
Now normally work only engine system, pause menu.