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.
When do you find it a good time to throw things in common proxy? I'm rather used to at my work where we follow the principal "One class should have a single responsibility". (I was a bit lazy here, rather than make a class dedicated to managing player quotas, I chose to give the save command that responsibility)