v0.0.20/21

• |NEW| Main menu 3d assets with skybox
• |CHANGE| Modular menus with clear logic

So,  I made modular menu system with possibility to easy expand logic and add more. 

For now I connected only a couple of buttons to load game, exit to main menu and quit game. All other buttons just placeholders, that show idea.

Next time plan to focus on game mechanics and update cheat menu, because I have a lot hidden functional, that is not easy to use with gamepad buttons without avoiding of intersection with game logic. 

So, make it clearer..