Hotfix v0.31.179

Another handful of kilobytes that make Learning Factory better:

• Zeppelins' highlight transparency decreased while they are in mid-air
  
• Zeppelin shadows transparency decreases while Zeppelins are high from the ground
  
• Decreased size of all Zeppelins (suggested by Milarky)
  
• 1 new hidden achievement
  
• Lots of bug fixes (kudos to Milarky, S'Kleer)