Adds credit awards, map unlocks, ship unlocks

[Jon-Cavaliere]

• Credits are awarded based on 3 aspect:
  • 1) base_creds - The base amount for completing a map
  • 2) silver - float that specifies time in seconds to beat for x2 and map unlock
  • 3) gold -float x 3 and map unlock

Map unlocks are saved as an integer that specifies the index of the most recently unlocked map. Maps are displayed as greyed out with locked info if their index is greater that unlocked_maps (State)

Adds Art:

• lock.png
• silver.png
• gold.png

• New Global State:
  • State.unlocked_maps
  • State.base_creds
  • State.silver
  • State.gold

[Jon-Cavaliere]

After merge resolution, map unlock and credits DOES NOT WORK. Fix in progress