Adding saving and loading screens with multiple save slots.

Also, remove combat button. Currently, the save and load buttons use the
combat icon, so new icons need to be created for the save and load
screen buttons.
Add dummy loading screen.

The game now starts in a dummy loading screen instead of the world map.
However, the code that waits for all resources to load and then switches
to the world map or load game screen still needs to be implemented.
Merge branch 'Adam'