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.
Usually anything that has different behavior when it's ran on the client/server (which is why they exist in the first place). When ran on the client (SP) there's really no reason to limit things and the save directory should be the already defined directory.

I also made a bit of a "typo". Just put the abstract of the method into common and then the implementations in the corresponding proxies, except for `getPlayerQuotaUsage`, that should be the same on both sides.