Mysterious Mining Monoliths

Adds purple monoliths to the mining asteroid, which will appear in
various locations spread far apart from each other. Touching them will
activate them, and once activated you can use them to travel between
active monoliths.

The teleport is AOE, so you can bring your ore box with you or
something.
Merge pull request #112 from CollenN/monolith

Mysterious Mining Monoliths