Implemented ladders.

Added ladders to each level (and changed the game to have 5 levels not
1) with placeholder images. You start on level 0 (top) and work down to
level 4 (bottom), you use the ladder tile to traverse between levels.
Also added a cooldown between tile usage because you would use a tile
twice when moving down, which moved you back up.
Merge remote-tracking branch 'upstream/master'
ignore crash logs
Add some ladder images
mess around with walls