Additive suit damage reduction

[marsolk]

Adds an alternative option for suit damage reduction, "Additive", where each suit gets a specific damage reduction value, and each value is added together to determine total damage reduction. Varia and Gravity Suits each provide +10% damage reduction, and Phazon Suit provides +30% damage reduction.

Examples:

• Varia or Gravity Suit alone provide 10% total damage reduction
• Both Varia and Gravity Suit provide 20% total damage reduction
• Phazon Suit and one additional suit provide 40% total damage reduction

staggeredSuitDamage property is changed to allow "Default", "Progressive", or "Additive" while maintaining backwards compatibility with boolean values.