Fixes https://github.com/turt2live/matrix-media-repo/issues/311

Fixes https://github.com/turt2live/matrix-media-repo/issues/271 at the same time

This should help memory some more. See https://github.com/turt2live/matrix-media-repo/issues/237

Theory is that by dumping the streams we'll relieve any bytes held on by the S3 libraries. 

Might reduce memory usage over time

Part of https://github.com/turt2live/matrix-media-repo/issues/209

Part of https://github.com/turt2live/matrix-media-repo/issues/209

Fixes https://github.com/turt2live/matrix-media-repo/issues/182

Fixes https://github.com/turt2live/matrix-media-repo/issues/178

There's a race condition where a stream might not be available if the media is remote and being downloaded. After a couple download attempts, it fixes itself. This will acquire a media stream if one isn't provided to ensure that a stream is always available to the consumer.

Fixes https://github.com/turt2live/matrix-media-repo/issues/142

Might be a fix for https://github.com/turt2live/matrix-media-repo/issues/92

Fixes https://github.com/turt2live/matrix-media-repo/issues/126

Fixes https://github.com/turt2live/matrix-media-repo/issues/20

**Caution**: This is a major migration that changes how files are tracked within the database. Although tested to ensure things won't go wrong, there is the possibility of something going haywire. It is recommended to run the following database commands before upgrading:

CREATE TABLE media_backup AS TABLE media;
CREATE TABLE thumbnails_backup AS TABLE thumbnails;

In the event you need to roll back, run the following:
DROP TABLE media;
DROP TABLE thumbnails;
CREATE TABLE media AS TABLE media_backup;
CREATE TABLE thumbnails AS TABLE thumbnails_backup;
DELETE FROM gomigrate WHERE migration_id = 7;

This will cause any files uploaded between upgrading and rolling back to be lost.

NOTE: The migration will take a while and runs on the first access of a file. If you have a lot of files, this could take a while.

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Fixes https://github.com/turt2live/matrix-media-repo/issues/106
Step towards https://github.com/turt2live/matrix-media-repo/issues/47

Future support will include deleting media that hasn't been accessed in a while

Downloads go through quite a few layers, and some of those layers are copy/pasted. Needs some refactoring, but it works.

Part of #58