Fixes https://github.com/turt2live/matrix-media-repo/issues/444

Also fixes a memory issue where we'd decode the entire image before deciding that the image is too small for thumbnailing.

Fixes https://github.com/turt2live/matrix-media-repo/issues/407
Closes https://github.com/turt2live/matrix-media-repo/issues/412
Closes https://github.com/turt2live/matrix-media-repo/issues/413

Closes https://github.com/turt2live/matrix-media-repo/issues/411
For https://github.com/turt2live/matrix-media-repo/issues/407

For https://github.com/turt2live/matrix-media-repo/issues/411

They are a shared resource, so treat them as such

Part of #45 - the only thing missing is a way to quarantine all media in a room

Fixes #10