Support proper uploading to s3

...ollers/thumbnail_controller/thumbnail_resource_handler.go

...a-repo/controllers/upload_controller/upload_controller.go

...live/matrix-media-repo/storage/datastore/datastore_ref.go

...matrix-media-repo/storage/datastore/ds_file/file_store.go

...ive/matrix-media-repo/storage/datastore/ds_s3/s3_store.go

...turt2live/matrix-media-repo/storage/startup_migrations.go

...thub.com/turt2live/matrix-media-repo/types/object_info.go

src/github.com/turt2live/matrix-media-repo/util/files.go

src/github.com/turt2live/matrix-media-repo/util/streams.go