power ups update

I added 4 powerups you can get by bringing one of the 2 largest rats into the game, the second largest will give you 1 random powerup and the largest will give you 2 random powerups.

the powerups include

• shake: shakes all the rats around a little (orange)
• delete all lvl 2 and lvl 1 rats (red)
• delete 1 rat of any kind: click the power up then the rat you want to delete (pink)
• upgrade 1 rat: click the power up then click a rat you want to upgrade (green)