More quota logic from filesystem proxy to storage wrapper

This re-implements the quota system as a storage wrapper and removes the quota fileproxy, as with the proxy the quota is applied transparently when using the filesystem api's.

This does however change the quota behavior from being filesystem-wide to storage-wide, meaning that only the main storage for each user (mounted at `/$user/`) is affected by the quota, any other mounted (or shared) storage will not be affected. Meaning that people no longer get storage deducted from their quota when mounting google drive, dropbox, etc.

cc @DeepDiver1975 @MTGap @karlitschek