Create model for planets

[morgajel]

Planets have

• name
• max mineable
• max gatherable
• max scavengable
• remaining mineable
• remaining gatherable
• remaining scavengable
• replenish mineable
• replenish gatherable
• replenish scavengable

We'll require an association table to link a planet to an item, as well as the method of collecting it and how plentiful it is.