adding structures.txt to mod
AmmoDepot structure changes

changed relevant tech from Cargo to ProjWeapons
ammo storage starts at 10 secs of production and increases with lvl
construction cost per bullet now static
mass now tied to build costs (and higher)
labor cost no longer static
AnalyzePlanet and Metal Gov changes

AnalyzePlanet updated to compute fuel/ammo production rates
Megal Gov updated:
- to no longer leave any fuel depots
- no longer build cargobay
- to only leave cargobay on 14+ slot planets
- to leave ammo depots as long as metal cost is locally produced