Update #61 - Mine balance update

This is a small update tweaking some numbers so the mine feels more rewarding to use. [b]Gameplay changes:[/b] [list] [*]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). [i]This only applies to newly created quests.[/i] [*]Decreased chance of getting non-standard quest items in quests by 20-40%. [*]Decreased unlock requirements for new zones in the mine. [/list] [b]Bugfixes:[/b] [list] [*]Fixed mine content disappearing in split screen. [/list]