List and Remove commands for quota management.

Finally got a chance to finish this off.

I've started out with an 8mb limit which feels like *HEAPS*. a 4096 chunk schematic took up 2mb.

It's not perfect in that if you have 7.99mb used, and then save a 1mb schematic, it will let you do that, but it won't let you save any more after that.
You can replace all usage messages with the `WrongUsageException`, I replaced that in the save command (shorter and makes the text red).