Draft: Feature/percentage based vehicle engines

Spreadsheet: https://docs.google.com/spreadsheets/d/1k7J-QHVbIiWgk87uUGgN_wGug1xJWMbvekZihUVJ0GM/edit?gid=34394673#gid=34394673
This changes vehicle engines script values to be percentage based (multiplicative) instead of additive (or whatever you'd call the mess that they were)
(this also contains a reformatting of the scripts so properties are grouped together which makes it much easier to read/modify)

Notable changes that aren't a direct result of percentage based conversion:

• Base Weight
  • APC: 15
  • LT/AFV: 30
  • Medium: 40
  • Heavy: 50
• Base Cost
  • APC: 10
  • LT/AFV: 20
  • Medium: 30
  • Heavy: 40
• Base Heat Capacity
  • APC: 90
  • LT/AFV: 100
  • Medium: 110
  • Heavy: 120

Notable changes that are a direct result of percentage based conversion:

• APC
  • researched engines are slightly slower
• LT/AFV
  • 3 Phase and Fission are slightly faster
• Medium
• Heavy Tank
  • Slightly faster
  • Better cooling

To Do:

• Increase weight on medium and heavy tank chassis to match the increase in engine weight.
• Think about stall on heat values, they might need to be increased.
• Review everything, twice.
• Playtest

Example of an engine's description:
Fission is 20% lighter, has 35% more horsepower and its top speed is 30% faster than standard engine, however it is twice as expensive. It dissipates as much heat as standard engine at idle but it dissipates 3 times as much at max.

(just to be absolutely clear this is not ready to be merged yet)