Update #61 - Mine balance update

This is a small update tweaking some numbers so the mine feels more rewarding to use.

Gameplay changes:

• Increased success rate for minerals (values have been adjusted so the overall income is the same)
  
• Item experience for Minerals now increases even if the attempt is unsuccessful.
  
• Quests can now only have one non-standard item (such as jobs, mines or production buildings). This only applies to newly created quests.
• Decreased chance of getting non-standard quest items in quests by 20-40%.
  
• Decreased unlock requirements for new zones in the mine.
  

Bugfixes:

• Fixed mine content disappearing in split screen.