Update just after the end of the jam

I updated the game after the end of the jam, giving two new files:

- Falling Islands - Game Jam version: the exact same project than the one when the game jam ended, with a Credits.txt added and useless files deleted.

- Falling Islands: The updated version of the game, with the following changelog:

• Islands now move
• A score has been added, it counts the number of islands that you avoided
• The time between two spawned islands is a bit random
• There is now a background color, to change from the dark grey default color given by Godot
• Fixed the Game Over label that was under the islands and misplaced
• Fixed a bug where the islands couldn't spawn if you went to the left too much