Begin signal path rewrite: prepare uploads; start MSC2246; new quota behaviour

CHANGELOG.md

README.md

api/routes.go

api/v1/create.go

common/config/conf_min_shared.go

common/config/models_domain.go

config.sample.yaml

database/db.go

database/table_expiring_media.go

database/table_reserved_media.go

database/table_user_stats.go

migrations/19_create_expiring_media_table_down.sql

migrations/19_create_expiring_media_table_up.sql

pipline/_steps/quota/check.go

pipline/_steps/upload/generate_media_id.go

pipline/create_pipeline/pipeline.go

util/mxc.go