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.
I was really impressed when I found it too. I'm going to keep it aside in my "useful snippets" folder.