Large Tent

I've added a large tent to the game, with a floor space of 3x3 and a total space of 5x5. 

To accomplish this, I added:
- An iuse function for the tent
- An iexamine function to take down the tent
- Two new furniture objects, groundsheets
- The actual json data in item_groups.json, furniture.json, and tools.json

The tent has 40 volume, making it just troublesome enough to outweigh its boon of space. The spawn rate, however, is identical to the smaller personal tent.