Powercraze 1.2

Major changes:

- Added a level selector to the main menu

- Added effect on powerup pickup! (Depending if it's good, neutral or bad)

- Changed the design of the powerups! (Again, depending if it's good, neutral or bad)

- Added trails to the players and disk!

Minor changes:

- Adjusted the disk's maximum speed
- Adjusted forced applied by the players to the disk