Refactored contract with fixed bugs and loopholes

[Van0k]

Main changes:

• Separated different business logic units into different contracts for better structural clarity.
• Added base contracts (Ownable, Freezable).
• Added SafeMath.
• Added ReferralProxy for referral investors to pay.
• Made main contract freezable.

Secondary changes:

• Cleaned up unnecessary variables and declarations.
• Reworked raiseCap to prevent a period when it is possible to move funds.
• Made some style improvements.