Added difficulty levels for challenge mode.
[list]
[*] Normal (default)
[*] Hard (skip 5 levels)
[*] Hard+ (skip 10 levels)
[*] Very Hard (skip 15 levels)
[*] Very Hard+ (skip 20 levels)
[*] Nightmare (skip 30 levels)
[/list]
You will get all rewards for skiped levels