Update sprite sheet

-Split wide sprites into single-tile-wide segments and rearrange them
Further simplify addition of new obstacles

-Merge Obstacle constructor and init method
-Add JSDoc comment for Obstacle class constructor
-Remove code to add obstacles since it no longer works
Check lethal property of obstacles in collision check rather than player's height
Update sprite sheet and source coordinates for Player and Prop objects
Correctly check for optional arguments in Obstacle constructor
-Store obstacles as multi-dimensional arrays
-Always use pixel coordinates for Player's position
-Remove collision detection