new critter rarity fields

[laugexd]

i propose 2 new fields to help with showing the rarity of critters:

• rarity value, this would be the integer version of the rarity field, which is currently a string for the visual representation of the rarity, this field would show 1 for the lowest rarity, 2 for the second lowest, so on and so forth, so it's easier for developers to visualize a rarity.
• true rarity, this would be the data mined spawn chance for each critter to spawn, shown as a floating point number in the range of 0 - 100