add save and load screen

[stolsky]

• [ ] create load screen to access from menu

• [ ] create save screen to access from game

• [ ] add save item to game screen

• [ ] add listener to show save icon

  • use visibility: hidden and pointerover to make visible

• [ ] add load icon to game screen

• [ ] add listener to show load icon

  • use visibility: hidden and pointerover to make visible

• use current act and scene name + date and time of saving

[stolsky]

similar to #6. will be in the same merge request.