Add support for quotas

api/r0/upload.go

api/responses.go

api/webserver/route_handler.go

common/config/conf_min_shared.go

common/config/models_domain.go

common/errorcodes.go

config.sample.yaml

migrations/17_add_user_stats_table_down.sql

migrations/17_add_user_stats_table_up.sql

quota/quota.go

storage/stores/metadata_store.go

types/stats.go